Oh what a good observation! I was wondering what might have caused that spike! (Other than just general data flukiness :) I'll have to go back through my list and see if I included a bunch of fics from that fest that year.

It's unfortunate that my list is idiosyncratic to me - I wish there was a way to search AO3 for this info, but while some authors will tag for top/bottom, there's still the whole "dating the fic" issue which I ranted about already. So I have to use my data to be sure, and there's always the chance it could be skewed. But your idea makes a lot of sense, so I'll look for that!