Well like said in the previous holiday, the next was in November. Funny enough, close around to the incident heh.
But anyways. Today, November 9th, is Monsters Inc.'s Founders Day. Pretty self explainatory heh heh.
Happy Monsters Inc. Founders Day then. 
Happy Belated Founders Day for Monsters Inc. I wish I knew how you knew these things, lol! 
Helps to have a good source heh heh 
To be honest, I had no idea until you made the first post about the “holiday”.
It’s where research gets you hehehe.
The next holiday is near the end…well not really the end…more like 3/4s of the way into December.
More proof of the phrase “it’s who you know not what you know”?
That’s more of a less-desirable way to describe it.