What happened to flags on 21 December
One flag in the atlas carries this date. The sentence under it is where that is written down, in its own article.
- Croatia 1990
The current flag and the coat of arms were officially adopted on 21 December 1990, about six (de facto) or ten (de jure) months before the proclamation of independence from Yugoslavia and a day before the Constitution of Croatia on 22 December 1990.
From Flag of Croatia on Wikipedia, as it read on 2026-08-29
How a day gets onto this site
A flag is here because a sentence in its own English Wikipedia article puts it on this date, and that sentence is printed above. Nothing was worked out from a year, and nothing was written for the occasion. Every sentence names the article it came from and the version of that article it was read in, so you can go and check it.
The calendar is still short rather than full. A third of the year has no page here, because a flag only gets a day when a sentence in its article puts something on one, and plenty of articles never do. Nothing is invented to fill the gap.