I originally posted this on the other site back when I took the picture, and it resulted in a lot of confused comments, especially from Americans, eventually getting removed by overzealous mods. Either way, I promise you that this date does not exist, and has never existed.
Remember, kids, not to ever compute dates yourselves. Use a library for that.
I’ve made that mistake a couple times, sending bills to people for things like April 31st. Have since swapped to letting python make calendars for me.