I suppose it could be intentional, meant as a mistake on Harry's part, but I've always thought the books come from his case files. That's the in-character way they're treated in the DFRPG, as well. From the marginalia there, it seems like each was written up at some unspecified time later (much later in the case of Changes, granted) after the case was closed.
Either way, pointing it out can either get it fixed in future editions, or maybe get a confirmation that it was intentional. Arguing about that sort of thing would be pointless and can only screw up the thread.
Thanks for mentioning the equinox/solstice thing, whichever way it turns out. I meant to ask about it myself. In my case, i have the audiobook, so for me there was a third possibility: maybe the draft Mr. Marsters was working from could have been slightly different, if it came from a version prior to the final edit.