The last one seems like it could also be problematic, how do you distinguish the 1960s decade from the literal year 196. In this case it’s kind of obvious since photography wasn’t very popular in the year 196.

Interesting question. From the Wikipedia article,

> ISO 8601 allows Gregorian dates from the introduction of the calendar on 15 October 1582.

https://en.wikipedia.org/wiki/ISO_8601#Dates