This may be too mundane and pointless even for this forum, but the window for celebrating the anniversary of February 30 is just today, so I hurried to post just in case.
When Europe converted to the Gregorian calendar, they needed to discard days, rather than adding extra leap days but what happened, I think, is this: Sweden came up with its own conversion plan, discarding a day (Feb. 29) every 4 years, but then changed its mind after a decade or so, so added an extra leap day, to get resynchronized with Julian-calendar Europe.
(PS: As I post it is Feb. 30, or if you prefer, March 1, in my timezone.)