Stuff like this is why I keep visiting here. I didn't know any of the books went into detail over McCoy's divorce. Thanks for mentioning that, now I'm curious about Planet of Judgement. You said it's the first time it's touched on, what other books go into detail about it? I assume there are differing, contradictory accounts, but that's not off-putting.
I guess the main one is
Shadows on the Sun by Michael Jan Friedman, although that's building on the version of McCoy's ex-wife (named Jocelyn) that was introduced in Vonda N. McIntyre's
Enterprise: The First Adventure (in which the couple is already bitterly divorced, but there's some background at least hinted at). It's also peripherally addressed in
Crisis on Centaurus by Brad Ferguson, which features Joanna McCoy. There are also some early comics that deal with McCoy's daughter and probably touch on the divorce -- Gold Key #40 & #43 dealt with a version of McCoy's daughter named Barbara, while Joanna McCoy appeared in #13 of Marvel's post-TMP series, possibly the best issue of that short run.
I'm surprised that The Final Reflection isn't on the list, but then I don't know how it counts in the context of when it came out as a milestone or innovative book.
It's certainly innovative -- the first Trek novel told as an in-universe work of historical fiction (a precedent later followed by
Strangers from the Sky to a partial degree), and the first in-depth exploration of a major alien culture from Trek, a precedent that would be followed by
The Romulan Way and
Spock's World.
While Christopher's assessment regarding Spock's World is not incorrect, I will admit that it was not what I was thinking of. Rather to me the novel represents the first time that a Trek novel attempted to grow beyond merely replicating the what was shown on the television and movie screen. With its divided structure, one chapter featuring a very atypical political story, featuring the Enterprise crew, wherein not so much as a shot is fired, but rather it is a rousing planetary debate and mystery story that holds all the action. Then the alternating chapter explores a period in Vulcan's history, starting literally with the planet's formation. Then we are shown pre-history, early history, a period akin to the renaissance, then the life of Surak is explored, and then the courtship of Spock's parents.
Actually
Spock's World was the second consecutive Diane Duane ST novel to alternate between present-day and historical chapters, the first being
The Romulan Way (in which the historical chapters were actually presented as a nonfiction monograph written by the main character featured in the present-day chapters). And its Vulcan history was expanding on what Duane had already established in TRW. They're essentially companion pieces.
And it certainly wasn't the first book to grow beyond replicating a TV episode or to tell an atypical story.
The Final Reflection absolutely counts in that respect.
First of all because the events contained in the book are referenced briefly in Spock's World, it represents the first time so far as I know that one author took anything in such a direct way from the work of another, foreshadowing the rather amazing interbook continuity that we have today.
Again,
Spock's World was far from the first book to do this. The
inter-novel continuity began to emerge at the start of 1985, when
Uhura's Song referenced the felinoid security officer "Snarl" from
The Entropy Effect, and
Shadow Lord referenced Sulu's backstory from the same novel. Later that year,
Dwellers in the Crucible drew heavily on both Duane's Rihannsu and Ford's Klingons, and in fact I believe it was the first time that Ford's or Duane's versions of those species were utilized by a different author. 1987's
Chain of Attack by Gene DeWeese was a loose sequel to Lee Correy's
The Abode of Life and included security chief Ingrit Tomson from J.M. Dillard's novels (who also appeared in
Spock's World). And A.C. Crispin's
Time for Yesterday, in April 1988, was the book that really tied the '80s continuity together, with references to the books of Diane Duane, Brad Ferguson, John M. Ford, Jean Lorrah, Vonda N. McIntyre, and Howard Weinstein.
Spock's World came out shortly after that, in September '88.
But more than that it is so far as I know the first time the books dove deeply into the history not just of the Enterprise and her crew as Enterprise did, but into the history of The Federation.
I hate to keep doing this to you, but no. The fictional-nonfiction
Star Trek Spaceflight Chronology from 1980 offered a version of Earth and Federation history that was the basis for
The Final Reflection's events a few years later.
Killing Time also delved briefly into the formative era of the Federation, in a different way.
The powers that be could have chosen to play it safe and not given permission for something so important to be shown in a novel, knowing that at some point in the future one of the movies or tv shows might contradict it.
That wasn't really a consideration back then, when there was only the occasional movie coming out. The early Trek novelists were a lot freer to imagine or redefine the larger universe however they wanted, because so much of it was still a blank slate. The attitude that tie-ins had to restrain themselves to avoid contradicting new canon didn't emerge until TNG was on the air and adding new canonical material on a weekly basis -- and until Richard Arnold started cracking down on the tie-ins to make sure they stayed in line with "Gene's vision."
Without Strangers ... I personally do not believe we would have gotten The Eugenics Wars, or Dayton Ward's novels following the fate of Mistral, or the Rise Of The Federation novels. Strangers proved there was in interest in stories showing how the universe we love so much came to be.
I'll grant that it was a formula-breaker and somewhat influential, but you're totally wrong to call it the first book to do any of these things.