I don't know where the idea that the Enterprise is the first Starfleet ship ever to undertake a five year mission came from, but it's been roundly dismissed since. (Real world because they were expecting to make 5 seasons?)
The phrase "its five year mission" could have suggested they were the first, perhaps, or alternately, that the Enterprise's particular task for the next five years, as opposed to, say, mapping the J'bruus Sector, is one of general exploration and discovery, along with whatever else they're needed to and able to assist with when asked.
Into Darkness depicts the five year mission as a brand new program, that no ship has ever had a five year mission (of this scope and focus) before. And perhaps in that reality, it's true; the Kelvin disaster may have delayed exploration in favor of securing current colonies, monitoring Romulan activity more than ever, and building the fleet/innovating in tech.
Back to the prime reality. According to PIC, Matt Decker had three five year missions on the Constellation, beginning in 2245. Plus 3x5, that's about 2260 - five years or so before Kirk. Pike had also been on a five year mission, leaving him too far away to participate in the Klingon War in DSC.
So what was it supposed to be in-universe, in TOS? New and unique or one of many?
https://memory-alpha.fandom.com/wiki/Five-year_mission
The phrase "its five year mission" could have suggested they were the first, perhaps, or alternately, that the Enterprise's particular task for the next five years, as opposed to, say, mapping the J'bruus Sector, is one of general exploration and discovery, along with whatever else they're needed to and able to assist with when asked.
Into Darkness depicts the five year mission as a brand new program, that no ship has ever had a five year mission (of this scope and focus) before. And perhaps in that reality, it's true; the Kelvin disaster may have delayed exploration in favor of securing current colonies, monitoring Romulan activity more than ever, and building the fleet/innovating in tech.
Back to the prime reality. According to PIC, Matt Decker had three five year missions on the Constellation, beginning in 2245. Plus 3x5, that's about 2260 - five years or so before Kirk. Pike had also been on a five year mission, leaving him too far away to participate in the Klingon War in DSC.
So what was it supposed to be in-universe, in TOS? New and unique or one of many?
https://memory-alpha.fandom.com/wiki/Five-year_mission