The Additional Manuscripts began on 29 September 2014. Scattered Ashes has an anniversary on 9th of March (five days after March the Fourth, KotOS Day). If you want moar things to celebrate I can provide you with the Shadow Anniversary, September 12th, and January 22nd, Strange Odd Shadow's birthday (if it doesn't seem ridiculous enough, it is unconfirmed if it's also Wiz's birthday). Hmm, anything else? We can celebrate September first for the Servant of Darkness. My joining of the KotOS was a historical moment, too, so here's 21 of November for you. Jonna made the topic of Imagination Infection on the 14th of February, if you're interested. The Chapter Zombies rose on the12th of March. We seem to have a peak of activity in March! :P And finally, I've got you what we should actually be expecting both for its importance and the fact it's the nearest thing: THE TWELVE DAYS OF DUCKZMASS!!! Or is it Duckmazz? Duckzmazz? I don't know.
From the 13th of July to the 24th are the Twelve Days of Duckzmass leading up to the 25th, Duckzmass (what? I only just noticed it's 25, too, exactly six months after/before Christmass. It's official, Duckzmass it is). Technically, the twelve days of Christmass are after Christmass, but it seemed more appropriate to call Duckzmass they day of the Duckination rather than the Day of the First Duck. Also, 25th!!!
Edit: It's interesting how I said six months when it's actually seven/five months! :P Still impressive.