PPatters: I can see that, but, in that case, I think that would have to be the point of the book, to fill in the blanks, answer some outstanding questions, or tie up loose ends (like with my Khan books).
For me, the goal in telling stories like
Ex Machina, The Darkness Drops Again, and
Forgotten History is to do just that, to explore the gaps. I've always been most interested in the parts of Trek continuity that haven't been explored, the ones that give me the most creative freedom. I first conceived of
Ex Machina (or the idea that eventually became that) years before I became a Trek author, during the era when the novels weren't allowed to have any real continuity or character growth. That kind of story where nothing really changed held little appeal for me. I thought I could make an end run around those restrictions if I focused on a known period of transition between two established endpoints, TMP and TWOK, and explored how the characters got from where they were in the former to where they were in the latter. That way I could have development and change within the limits of canon. (Though these days I suspect that if I had pitched the novel back then, it would've been rejected anyway; it's probably for the best that I didn't get involved with Pocket until the restrictions of the '90s had relaxed.)
I also prefer the TMP era because I think it has a lot of unrealized potential. TMP was a flawed movie from a story standpoint but created a rich visual and conceptual world; the
Enterprise and its crew have never looked so fascinating, and it's disappointing that we didn't get more films that conveyed the same rich sense of environment that TMP created.
Defcon: As for the plausbility of squeezing so many adventures into a 5YM, well, that's just the nature of long-running series. How many cases could the Hardy Boys or Nancy Drew really investigate before they grew up? How many innocent clients could Perry Mason be expected to defend over the course of his career? How many "perfect" murders took place on Columbo's turf? How did Doc Savage find time to save the world 181 times?
I'll give you the Hardy Boys and Nancy Drew -- also the Marvel Universe -- but in the case of Perry Mason, Columbo, and the like, those aren't expected to be crammed into a finite span of time. Sure, it's unrealistic that a criminal attorney would have over two dozen murder trials per year (or rather, preliminary hearings, since Mason almost always cleared his clients before the jury trial even began), but at least it's all assumed to be happening in real time. When Perry Mason and Columbo were revived in the '80s/'90s, they had aged accordingly, and their new adventures weren't all alleged to take place in the same 5-year span as their old ones.
So we're talking about two different kinds of implausibility here. It's implausible that one starship would get into mortal danger an average of once every two weeks, rather than having just the occasional dangerous situation among lots and lots of routine missions and downtime -- but at least it's actually
possible to fit the 79 episodes of TOS into the span of three calendar years. It may strain credibility, but at least it doesn't violate physical law. But once you get to the point that the sum of the durations of all the "5-year mission" stories out there exceeds 1825 days, then it becomes outright impossible that they all took place. And that's a lot more disbelief to suspend.
So given that the 5YM era is so crowded already while the post-TMP era is a wide-open, mostly empty space, why not set stories there?