Star Trek, through their somewhat haphazard way of doing things, has created quite a mess. This is my theory on how to make sense of it.
First, we go back to the beginning to see how it started, unraveled, and then began to make sense.
1701 - Matt Jefferies intended this number to be the first ship of the 17th design. That didn't even last the first season. In Court Martial you get 1700 and a host of other registries on a wall in the Commodore's office. While that 1700 and the Constitution have never been matched in canon, that seems a certainty. Then in the 2nd season you have the Constellation - 1017. This is just a remix of the Enterprise registry. After the series ended, and using production information, Greg Jein theorized that the list of ships in the Commodore's office were the Constitution Class. He misread at least one number, but he matched all of them up to the official name list.
The 70's gave us Franz Joseph's General Plans and Technical Manual and a slew of classes and names. In the 500's and 600's you have the destroyers and scouts. 1700's and 1800's are the Constitution Class Heavy Cruiser. The 3800's and 3900's are the transport/tugs. And a handful of the lower 2100's are the new Dreadnaught. Not really canon until some of these pages appear on screen as computer displays. And much later the long followed paired nacelle rule is broken in canon opening the door to these 1 and 3 nacelles designs. The next 3 ships we see follow along. Reliant is 1864 (right after the Constitution Class), Grissom is 685 (right after the Hermes Class Scouts) and Excelsior is 2000 (between the Constitution and Federation Classes.
The 80's gave us the FASA role playing game and their list of ships. The Larson Class destroyer in the 4300's and 4400's. Chandley Class Frigate in the 2300's and 2400's. The Loknar Class in the 2700's. Plus many other classes lacking registries.
Then we get a new Star Trek series and things really get interesting. The first few ships have the standard 4 character registries. Hood 2541, Stargazer 2893, Repulse 2544, Hathaway 2593. And at first we can't really see the registries on screen, even though the models were often changed. But then we start seeing even more ships appear on computer displays listing registry and class and the numbers quickly climb. Soon they abandon the 4 character registries for 5 character and by the end of TNG 7 years later we get Voyager 74656.
So, what do they mean. Is there a pattern. Well, they tried, but they didn't want it too clear so while there is a general pattern, it truly is somewhat random.
So how do we go back and make some sense of it. Especially in light of the Constitution Class and Excelsior Class having such a wide range of registries.
Constitution Class: 956, 1017, 1223, 1371, 1647, 1657, 1664, 1672, 1697, 1700, 1701, 1703, 1709, 1710, 1715, 1717, 1764, 1831, 1856, 1868, 1895, 2014, 2048, 1701-A.
Excelsior Class: 2000, 2541, 2544, 2573, 2582, 13958, 14232, 14598, 14934, 18253, 34099, 38907, 38995, 38997, 40521, 42111, 42136, 42285, 42296, 42768, 42857, 42995, 43305, 44278, 50446, 62043, 72007, 1701-B.
Really, there are several possible explanations. What I am about to get into is how I see it. My mind first went to Franz Joseph's nice complete lists. But when you look at real world construction of ships (and planes because planes happen in larger numbers like Trek ships where ships tend to be in much smaller numbers) you find skips, jumps, cancellations, conversions, and a lot of oddities. I've applied that to Trek ships and gotten the following.
First, the ships are planned for. This is the stage where Starfleet budgets and contracts for the ships. The reality becomes different. By the time of TOS, the Federation is a century old. In that century, ships have been built (of designs we can only imagine) and some have been cancelled, or postponed, or switched around. So when they go to build the Constitution Class, they start with 1700 as intended, but when the first ships prove so successful they convert some cancelled or unfinished hulls to the new design. So the main group are all 1700's or 1600's with the Constellation as 1017 and the Republic as 1371. And I take the pages of FJ's Tech Manual as the original order. They didn't make that many, but they made a lot more than 12. In TOS the lose 4 ships on screen and indicate that 3 others have been lost. That kind of attrition led me to make a list where there are 30 Constitution Class ships that have been built by TOS (only 13 left in service) and another 50 built before last of the class was built. For replacements, the registry is whatever is hanging out there unsued.
To extend that to the Excelsior Class, you first need to identify the differences and similarities. The Constitution Class was built over a 40 year period. At its peak there are up to 6 being built at once. Most of the time one or two. For the Excelsior you have a class in service for a century instead of just 50 years. Either more were made up front indicating a faster build program or they were built over a longer time. My guess is the latter or both. The Federation has grown and there is more to explore. There are also more classes. The Constellation Class is also in service with a handful making it to the 80 year mark. But the Excelsior is more of a direct replacement for the multi-role Constitution Class. Assuming that they built them in similar numbers and for a longer time (as the registry numbers indicate) there could be 500 or more of them. Also assuming that a lot of them didn't survive and some of that number are just replacements.
So what does that say about the registry numbers? That as Starfleet added new numbers at the top, there was room to build a few more Excelsior Class ships (and Miranda Class and Oberth Class as those follow a similar registry pattern). Either Starfleet was trying to keep a certain number or they needed more ships to fill that role.
The other question about the registry number is what is it? If it is a registry number, is that like a serial number or is it like the ship designation in the US Navy. A serial number is permanent and never changes. That kind of is derailed by 1701-A and similar registries. I think it is a commission registry. So when a ship has been decomissioned, it can come back with a different registry. Take the Excelsior Class U.S.S. Hood. The model was labeled 2541. But when it shows up on screen a couple seasons later the number 42296 appears. A plausible scenario is that the first ship was lost and they pulled another ship out of storage and re-registered it with the new number. I think the same thing happened to the Enterprise B. It was retired like the Enterprise A and when Starfleet needed a ship, the upgraded the weapons and gave it a new registry and name - U.S.S. Lakota NCC-42768. And notice how both ships have registries in the same 42xxx range.
So within any given time frame a ship of any class can have just about any registry number. When Starfleet expands the registry list for new ships, then a ship of an older class can be built or recommissioned with a new registry in the new ranges. So the original range was under 5000. Nothing in TOS or the OC movies goes above that. Then it is expanded at some point to over 10xxx and you have some more Excelsior Class ships and the U.S.S. Ambassador. By TNG they are at 7xxxxx. So there is somewhat of a chronology to the numbers, but at the same time they are random. And this works going backwards from TOS. The destroyer Scouts in the 500's and 600's were skipped for some reason and the classes between NX and Constitution fit in there somewhere. And the straggler numbers for the lower registry Constitution Class were extra numbers put in use rather than wasted.
First, we go back to the beginning to see how it started, unraveled, and then began to make sense.
1701 - Matt Jefferies intended this number to be the first ship of the 17th design. That didn't even last the first season. In Court Martial you get 1700 and a host of other registries on a wall in the Commodore's office. While that 1700 and the Constitution have never been matched in canon, that seems a certainty. Then in the 2nd season you have the Constellation - 1017. This is just a remix of the Enterprise registry. After the series ended, and using production information, Greg Jein theorized that the list of ships in the Commodore's office were the Constitution Class. He misread at least one number, but he matched all of them up to the official name list.
The 70's gave us Franz Joseph's General Plans and Technical Manual and a slew of classes and names. In the 500's and 600's you have the destroyers and scouts. 1700's and 1800's are the Constitution Class Heavy Cruiser. The 3800's and 3900's are the transport/tugs. And a handful of the lower 2100's are the new Dreadnaught. Not really canon until some of these pages appear on screen as computer displays. And much later the long followed paired nacelle rule is broken in canon opening the door to these 1 and 3 nacelles designs. The next 3 ships we see follow along. Reliant is 1864 (right after the Constitution Class), Grissom is 685 (right after the Hermes Class Scouts) and Excelsior is 2000 (between the Constitution and Federation Classes.
The 80's gave us the FASA role playing game and their list of ships. The Larson Class destroyer in the 4300's and 4400's. Chandley Class Frigate in the 2300's and 2400's. The Loknar Class in the 2700's. Plus many other classes lacking registries.
Then we get a new Star Trek series and things really get interesting. The first few ships have the standard 4 character registries. Hood 2541, Stargazer 2893, Repulse 2544, Hathaway 2593. And at first we can't really see the registries on screen, even though the models were often changed. But then we start seeing even more ships appear on computer displays listing registry and class and the numbers quickly climb. Soon they abandon the 4 character registries for 5 character and by the end of TNG 7 years later we get Voyager 74656.
So, what do they mean. Is there a pattern. Well, they tried, but they didn't want it too clear so while there is a general pattern, it truly is somewhat random.
So how do we go back and make some sense of it. Especially in light of the Constitution Class and Excelsior Class having such a wide range of registries.
Constitution Class: 956, 1017, 1223, 1371, 1647, 1657, 1664, 1672, 1697, 1700, 1701, 1703, 1709, 1710, 1715, 1717, 1764, 1831, 1856, 1868, 1895, 2014, 2048, 1701-A.
Excelsior Class: 2000, 2541, 2544, 2573, 2582, 13958, 14232, 14598, 14934, 18253, 34099, 38907, 38995, 38997, 40521, 42111, 42136, 42285, 42296, 42768, 42857, 42995, 43305, 44278, 50446, 62043, 72007, 1701-B.
Really, there are several possible explanations. What I am about to get into is how I see it. My mind first went to Franz Joseph's nice complete lists. But when you look at real world construction of ships (and planes because planes happen in larger numbers like Trek ships where ships tend to be in much smaller numbers) you find skips, jumps, cancellations, conversions, and a lot of oddities. I've applied that to Trek ships and gotten the following.
First, the ships are planned for. This is the stage where Starfleet budgets and contracts for the ships. The reality becomes different. By the time of TOS, the Federation is a century old. In that century, ships have been built (of designs we can only imagine) and some have been cancelled, or postponed, or switched around. So when they go to build the Constitution Class, they start with 1700 as intended, but when the first ships prove so successful they convert some cancelled or unfinished hulls to the new design. So the main group are all 1700's or 1600's with the Constellation as 1017 and the Republic as 1371. And I take the pages of FJ's Tech Manual as the original order. They didn't make that many, but they made a lot more than 12. In TOS the lose 4 ships on screen and indicate that 3 others have been lost. That kind of attrition led me to make a list where there are 30 Constitution Class ships that have been built by TOS (only 13 left in service) and another 50 built before last of the class was built. For replacements, the registry is whatever is hanging out there unsued.
To extend that to the Excelsior Class, you first need to identify the differences and similarities. The Constitution Class was built over a 40 year period. At its peak there are up to 6 being built at once. Most of the time one or two. For the Excelsior you have a class in service for a century instead of just 50 years. Either more were made up front indicating a faster build program or they were built over a longer time. My guess is the latter or both. The Federation has grown and there is more to explore. There are also more classes. The Constellation Class is also in service with a handful making it to the 80 year mark. But the Excelsior is more of a direct replacement for the multi-role Constitution Class. Assuming that they built them in similar numbers and for a longer time (as the registry numbers indicate) there could be 500 or more of them. Also assuming that a lot of them didn't survive and some of that number are just replacements.
So what does that say about the registry numbers? That as Starfleet added new numbers at the top, there was room to build a few more Excelsior Class ships (and Miranda Class and Oberth Class as those follow a similar registry pattern). Either Starfleet was trying to keep a certain number or they needed more ships to fill that role.
The other question about the registry number is what is it? If it is a registry number, is that like a serial number or is it like the ship designation in the US Navy. A serial number is permanent and never changes. That kind of is derailed by 1701-A and similar registries. I think it is a commission registry. So when a ship has been decomissioned, it can come back with a different registry. Take the Excelsior Class U.S.S. Hood. The model was labeled 2541. But when it shows up on screen a couple seasons later the number 42296 appears. A plausible scenario is that the first ship was lost and they pulled another ship out of storage and re-registered it with the new number. I think the same thing happened to the Enterprise B. It was retired like the Enterprise A and when Starfleet needed a ship, the upgraded the weapons and gave it a new registry and name - U.S.S. Lakota NCC-42768. And notice how both ships have registries in the same 42xxx range.
So within any given time frame a ship of any class can have just about any registry number. When Starfleet expands the registry list for new ships, then a ship of an older class can be built or recommissioned with a new registry in the new ranges. So the original range was under 5000. Nothing in TOS or the OC movies goes above that. Then it is expanded at some point to over 10xxx and you have some more Excelsior Class ships and the U.S.S. Ambassador. By TNG they are at 7xxxxx. So there is somewhat of a chronology to the numbers, but at the same time they are random. And this works going backwards from TOS. The destroyer Scouts in the 500's and 600's were skipped for some reason and the classes between NX and Constitution fit in there somewhere. And the straggler numbers for the lower registry Constitution Class were extra numbers put in use rather than wasted.
Nobody even knew then how Voyager would evolve as a series, and clearly the two names aren't even close to sounding confusingly similar. Likewise, we got a single Intrepid class ship in DS9 and we never got to see Sovereigns, because fans apparently can't handle them not necessarily being the Enterprise-E.
But I also don't think it's possible to assign any sort of chronology to them either, for the same reason. The "block" system is the most practical one for my personal head canon. 
It's obvious that whatever sources you using are inaccurate, to put it politely. CVN-65 launched with eight reactors and she was decommissioned with eight reactors. Which were de-fueled by 
