Treating birthdays on Feb 29 as if they happened on March 1 in non-leap years is wrong in places like California and New York -- at least probably most of the time, because while I already knew that, I didn't appreciate how deep the rabbit hole actually goes.
* https://leginfo.legislature.ca.gov/faces/codes_displaySectio...
* https://www.nysenate.gov/legislation/laws/GCN/58