It appears to be "official" that there is 12 years between TMP and TWOK. But TWOK has the one connecting date that makes sense with no fudging or hand waving: It's 15 years between Space Seed and TWOK. Because it was 15 years between the episode Space Seed and the film TWOK.
I think I discussed this earlier in the thread -- the Okuda
Chronology put TWOK 18 years after "Space Seed" for unclear reasons, and my best guess is that they felt TFF had to be more than 20 years after "Balance of Terror" to fit the Nimbus III backstory. Although I think it would've made more sense to round the Nimbus III date downward (or assume it was in Nimbian years rather than Earth years) than to add to the TWOK date. But we've been stuck with that dating for an awfully long time now.
Yes, I agree. I am saying it would have been proper for a mention of something from TMP in WOK such as a line of dialogue referring to: V'Ger, Decker, Ilia or whatever.
Well, one can take the reuse of the same ship and spacedock models, sets, props, and certain costumes (spacesuits, radiation suits, security armor) as evidence of continuity, as well as the use of the same department colors on the uniforms and the same arrowhead-and-circle version of the insignia. And I see Spock's more relaxed, serene personality in TWOK and afterward as an outgrowth of the emotional epiphany he had in TMP. Without learning the value of "This simple feeling" and the barrenness of pure logic in TMP, he wouldn't have been able to express his friendship for Kirk so openly and casually in TWOK, or to say "Logic is the beginning of wisdom, not the end" in TUC. So the evidence is in the character continuity.
Also, the character of Jedda (on Carol's Genesis team) was scripted to be a Deltan (and depicted as such in the novelization), though he looked human in the final film. So clearly Harve Bennett was willing to pick up on some ideas introduced in TMP.
At first, I was going to say I didn't think it would've been proper to mention the V'Ger incident, given that a dozen years had passed. Surely they'd had a whole bunch of other adventures in the interim, so it would be contrived if they just happened to be thinking of that particular long-ago one. But then I thought that maybe when Carol was defending Starfleet to David, she could've said something about how they saved Earth from V'Ger -- since the near-destruction of Earth is the sort of thing that would probably be talked about for a long time thereafter, like how Americans still talk about 9/11. That would also have been an opportunity to establish how much time had passed since the previous movie. But of course, they preferred to largely ignore TMP, or at least be agnostic about it.