Fun to think about, but in the real world, no question neatly divides people, even the gender one. To quote Reddit's u/tailcalled[1], the exo-software/meatspace world is even less standardized than the software world: Falsehoods programmers believe about gender: http://www.cscyphers.com/blog/2012/06/28/falsehoods-programm... Falsehoods programmers believe about names: http://www.kalzumeus.com/2010/06/17/falsehoods-pr…
> Months have either 28, 29, 30, or 31 days.
Does hold true: months do have 28 to 31 days, by definition. If someone wants my Gregorian date in a different calendar system, then we must convert, but that a display issue. Otherwise, we're comparing apples and oranges, and of course all bets are off.
It's kind of like time: the hour "2 AM" never repeats itself on random politically appointed days, because I have chosen to store timestamps in UTC. If someone wants to see that timestamp in "PST" (or America/Los_Angeles), then that's a display issue that can be accommodated, but it does not suddenly violate the fact that "2 am" never repeats in UTC.
Of course, in real life, people don't know what timezone their date is stored in and things love to break randomly on DST switch-overs or leap days or the ends of leap years.