Now a few corrections:
"Cannon" was a Quinn Martin production, starting in 1971, by which point Desilu was just a fond memory.
And, it was Bob Justman who was in a panic over the show not being able to make its airdate, and was preparing to send a letter to the network, at which point either Roddenberry or Solow, probably both, told him that under no circumstances was he to utter a word to the network about their schedule problems. Also, Justman raised his concerns pretty early in the production, because he was enough of a genius that he could tell, at the amount of time they were taking to complete episodes, they were gong to hit the wall at such-and-such time, which is precisely what happened. But because he raised his concerns early, Solow and Roddenberry had plenty of time to make contingency plans.
It's important to note here that Solow's job was to, essentially, run herd on the various shows under his purview, to make sure they're doing their jobs and not wasting the studio's and network's money (I have it on good authority that Solow was also drawing a paycheck from NBC, to make sure Crazy Gene wasn't about to spend them into the poorhouse). These shows included M:I, Mannix, and probably a few others besides Star Trek, so aside from periodic visits to the office to see if anything was done regarding Justman's airdate concerns, there's not a helluva lot he could do personally; he was just too busy. It was all up to Roddenberry and his staff.
Now, since Desilu was hammering Roddenberry to find some way to use "The Cage", and recoup some of the costs of what was at the time the most expensive television pilot ever shot.
Remember, one of GR's greatest strengths as a producer was being able to use the available resources in strange and innovative ways to get a show out of a jam.
Need to get the entire crew out of the way for the bulk of an episode and just leave your four or five main characters and guest stars? Well, shrink everyone down to the same shape as this little paperweight on my desk.
Need an alien plant and the greenhouse just doesn't get it? Pull it up by the roots and stick it back in the ground upside down. THERE'S your alien plant!
The Marines are yanking their technical adviser because you dared to mention Vietnam in an episode? Get out there and start training the extras on some basic marching drills.
So, when television show is faced with the prospect of not making its airdate, the options boil down to three options:
1) Air a rerun.
2) Put together a clip show.
3) Pray for two weeks of preemptions.
For a new show, options 1) and 3) are problematic at best, especially if you're struggling in the ratings, and normally 2) isn't an option because you haven't got enough footage in the can yet to do the old "Say, remember when we..."(cut to five flashbacks from previous episodes) routine. But Star Trek had over an hour of unseen footage, namely "The Cage". So, GR went off to write what soon became known as "the envelope", as in the envelope marked
"OPEN ONLY IN CASE OF IMMINENT NUCLEAR ATTACK!" that's kept in the office safe "just in case."
So, production chugs along, and sure enough, they hit that wall Justman had been warning about. To show you how concerned GR was, he happened to be on vacation in Hawaii at the time.
Time to go get "the envelope."
The result was not just a clip show, not just a clip show with previously unseen footage,
but a TWO PART CLIP SHOW!
Not only did they gain the time you generally get from putting out a clip show,
but another week on top of that, which to a time-starved show like Star Trek is more precious than gold pressed latinum.
And I'm pretty sure the history of this episode was pretty honestly related in "The Making of Star Trek" back in 1968.
As for how he described it in his lectures, I'm pretty sure GR's exact words were...
Gene Roddenberry said:
"We made the first pilot, which was rejected for being too intellectual for you slobs in the television audience. It then went on to win the international Hugo Award, but then many things rejected by networks would win awards!"