Oh, novel day sounds great! Looking forward to that already.
Hm, for NezuShi date, maybe something with 12 and 4, if you're going with that 'shi' also meaning four with a different kanji? 12 because that's the age they met, and four would also tie in nicely because of the four-year time gap in that case. April and December are both not too close to September, either. Just throwing this out there, sorry for barging in!
(Shame we have so few confirmed birthdays for the characters... that would be a bit easier to work with, haha.)