All this "speculation" (if one can use that term to refer to possible unknown actions of fictional characters) about the activities and motivations of Kirk pre-TWoK is useless. Occam's razor, people. The most parsimonious solution is that TWoK did indeed "overwrite" TMP (as someone upthread put it) - and, moreover, that Paramount at first supported this, hence avoiding the use of II not only in the original release prints but in the pre-release publicity and the cover of the tie-in novel, but then chickened out for marketing reasons and retroactively called the film II in later release prints and home video, as well as in ads and posters upon release.
(Oddly, there is one detail that doesn't fit: The novel does squeeze in a few peripheral references to TMP, none of which are necessary to the story. Of course the novel also has Spock's coffin burning up as it enters the Genesis planet's atmosphere...)
er, but ignoring something doesn't mean overwriting it. Also, two changes from TMP seem to affect TWOK- Spock's epiphany at the end of TMP seems intended to be the reason for the more comfortable and at-ease Spock in TWOK, also Kirk's still an admiral.
The Undiscovered Country doesn't acknowledge anything about TFF, but that doesn't mean that we were supposed to regard that as meaning that TFF never happened.(despite what some might wish to think)