You're probably right, but if some official publication like, let's say, the novelization, comes out with a timeline in the first couple pages that places ep7 at 40 years post-Jedi, is anyone really gonna go back to this moment from what'll then be 21 months earlier and really care?

I mean, as long as they don't bring up an exact number in the actual movie (just as they didn't bring up exact numbers in the OT except for Ben's "a thousand generations" line about the Jedi Knights), it truly won't matter if it's officially 40 instead of 30.