Kinda like those systems that went down on Feb 29, 2024. I mean, how does an app in the 21st century not handle leap day? Yet it happened.
We'll always have programmers that have less than 4 years experience programming and hadn't even considered leap days when programming "This should happen every last day of the month" or whatever.
One would think libraries would catch this one way or another, but some people are hellbent at doing things their own way and then... Well.
Or, you know they considered it because they left a comment in their code like // TODO: Handle leap year LOL
Just as bad. Don’t roll your own time handling code.