Date math vs. invalid dates

The function performs a certain amount of date mathematics

• now -1 months

seems the be the only non-disputable example of say date math expression, while the others like

• January 0 2008
• February 29 2007

could be called rather invalid dates. See bugs e.g. T178175, T321989, T411471. —mykhal (talk) 08:30, 3 December 2025 (UTC)