I've mentioned this around here before, but I've always suspected that the Okudachron dates for ST II-V were spaced out as they were to accommodate additional stories in that era if one were so inclined. They're not canon, obviously, but this allows you to include them if you want (which I do, for a lot of the comics) and not worry about it too much if you don't.
From what I remember, the 2286 dating of
Star Trek IV was apparently derived from the original TNG bible or something, with possibly the Okudas or the series producers (or both) either counting forward exactly 300 years from the movie's release date (1986/2286), and then applying Roddenberry's "78 years later" timestamp to TNG season one, or else the other way around, with the "2364" date mentioned by Data in "The Neutral Zone" forming the basis for the 2286 positioning (2364-78 = 2286).
Plus there's the onscreen dialogue in TNG's season three premiere "Evolution," mentioning that the last system-wide failures aboard a starship occurred "79 years ago," which seems to be an obvious nod/reference to the then-recently-theatrically-released
Star Trek V from just a few months earlier that summer, giving us a canonical datestamp of 2287 for that movie (2366-79 = 2287).
It's the 2285 dating of
The Wrath of Khan and
The Search for Spock that seems to be a bit more arbitrary (outright ignoring both of the "fifteen years" dialogue-references in the second film), although to be sure, there
is the "2283" onscreen mention (regarding Romulan ale fermentation) which seems to provide something of a potential canonical bottom-floor for the whole thing, at least.
(Vornholt's
The Genesis Wave isn't the only story dating the events of
Star Trek IV back into 2285, contrary to the Okuda chronology -- the Spock and McCoy volumes of David George III's
Crucible trilogy also use a 2285 dating for the fourth movie's events. These two series both appear to be uncommon outliers, though.)
Except for "Choices," I've always thought of these as taking place in a timeframe after ST V, because (I guess) I still don't like thinking of there being a tonne of additional Enterprise-A adventures between IV and V.
There actually truly aren't that many Kirk-stories set during 2286 at all, and only two novels in total (the
Enterprise-A sections of
Unspoken Truth, and
Timetrap, in my own continuity), plus "Scotty's Song" from SNW.
Pretty much all of the DC Vol. 1 stories set post-TVH (including the "Retrospect" annual) I tend to place prior to the 2287 framing-story sections of
To Reign in Hell (Greg Cox's third Khan novel) due to that wraparound's immediate pre-TFF setting, and the implication that the 1701-A had finally finished up its shakedown missions from the preceding year.
The great thing is, between the DC Vol. 1 stories and the scant couple of prose tales we have onhand, there are roughly
just enough stories there to decently fill out that initial shakedown-year prior to the fifth movie...but yet not
too many, either. It's pretty well-balanced, all things considered.
Since this came out concurrently with DC Volume 2, it never felt like it needed "fudging" to me--I just assumed it took place in between issues on the ongoing comic, which were all set after ST V.
Indeed, plus there's the whole Stephen Garrovick-factor present, which pushes the graphic novel to absolutely no earlier than 2287, post-TFF, if one counts
In the Name of Honor in their personal continuity.
Plus there's also Spock's remarkably-specific dialogue ("Twenty-five years, one hundred seventeen days") regarding his and McCoy's first service together aboard the
Enterprise in the graphic novel, which moves the story back even further to 2289, if one counts
Enterprise: The First Adventure there and retroactively applies the dialogue within the modern Okudachron-context (it also being implied that Sulu's captaincy-promotion was extremely close at hand).
Due to the lack of Kor's forehead-ridges and Sulu's rank,
Debt of Honor can't take place any later than, say, October/early November of 2289, though, and prior to
Excelsior: Forged in Fire.
It's those pesky early-'90s continuity assumptions which come into play a tiny bit here, regarding Gracie's calf, but again, this one little aspect seems be overshadowed by the preponderance of other dating-cues present in the story which vastly outnumber it. It's pretty easily ignorable if one chooses.
I share in the hope that stories like The Rift get included, though...another story that (being written by Peter David, onetime writer of the comic) felt like it would take place in between those stories.
Same here, and I imagine it likely will, considering that a number of later, modern Litverse tales reference it (including Margaret Wander Bonanno's
Burning Dreams).
You bring up another interesting subject here, concerning the placement of
The Rift with regards to the DC Vol. 2 run of stories (specifically, the post-TFF relaunch) -- from approximately issue #1 all the way up through issue #12 (the conclusion of the "Trial of James T. Kirk" storyline), there really isn't any storyline-room to speak of in which to slot in both
Probe and
The Rift, continuity-wise, unless one were to place them not long post-
Star Trek V, prior to the DC relaunch.
The roughly four or five major storylines comprising those dozen issues all take place contiguously with one another, sharing carried-over plot threads and supporting characters that are crucial to the flow of that run, and it's finally only in issue #12 (the ending of the trial storyline) that the first real "break" appears that might allow one to place other standalone tales deeper into 2287 (which is where VotI places
Probe and
The Rift).
Of course, again, it might also be possible to place these stories
before the DC relaunch, in between
In the Name of Honor and "The Return!" (DC Vol. 2, issue #1), but I've never really had a problem with VotI's placement of those (although again, there are a couple of those early-'90s continuity bugaboos in
Probe that don't quite jibe with the Okudachron).
That said, it's the hard, concrete
Star Trek V references in that novel which pretty conclusively date it following the events of the fifth movie, and one kinda just has to willfully ignore the other inconsistencies (which were, as
Christopher mentioned, an unfortunate artifact of multiple authors and multiple rewrites).