I don't know where to find more info other than in the usual places (AllEarsNet.com, Mouseplanet, etc...). Do you remember the Tea Party in Alice in Wonderland. The Mad Hatter threw an "unbirthday party". It is based on the idea that there are 364 "unbirthdays" in the year and only one birthday. Why not celebrate the unbirthdays since there are so many of them?
I know they do the Unbirthday Parties at various locations and usually do something with it if the Mad Hatter and Alice are around.
HBC