Actually, it seems like the author had two intents which are now contradictory, based on what's being described. (I have to go by this, since I haven't read The Better Man.)
On the one hand, the novel is supposed to be two years after TMP. On the other, it's supposed to be 18 years after 2255...which (at the time that book came out) would've been the same thing, based on official sources. The date for TMP has moved forward since then, but I would personally go with Jsplinis's instinct to maintain the novel's placement relative to TMP.
the book is positioned both 18 years after the flashbacks and 2 years after TMP, but the latter is far, far less important to the story and gets far fewer mentions in the text. It is not essential to the story that 24 months have elapsed since V'Ger or that they're wearing the TWOK uniforms. Those are both alluded to in passing, but they're incidental. But it is extremely important to the story, and mentioned quite a few times, that the central character who's suspected of being McCoy's daughter has just turned 18 years old, and it's made quite clear that he was on her mother's planet in 2254. (And McCoy's age in 2254 is given based on his birthdate as calculated from his canonical age stated in "Encounter at Farpoint.")
So it's a matter of priorities. The interval since the flashbacks is immensely more important to the story than the interval since TMP. The former is a critical plot point that comes up repeatedly, while the latter is an incidental bit of detail that gets a handful of passing allusions.