[lozaning]

Reactive snarky comment:

No it didn't : https://en.wikipedia.org/wiki/ISO_8601

Specifically 4.3.11 defines the start of a decade as any year where [year]%10==0.

[unnouinceput]

there is no year zero. Let that sink it

[ac29]

There is in ISO 8601: https://en.wikipedia.org/wiki/Year_zero

[unnouinceput]

And how many calendars use it? Lemme give you a hint, it's the same number as the the year in question

Also there is no day 0 of the month, no month zero of the year. It's how calendars work.