What happened to flags on 17 December
One flag in the atlas carries this date. The sentence under it is where that is written down, in its own article.
- Taiwan 1928
The modern flag was made official by National Emblem and National Flag of the Republic of China Act (中華民國國徽國旗法; Zhōnghuá Mínguó guóhuī guóqífǎ) on 17 December 1928, after the successful Northern Expedition that toppled the Beiyang government, though the Five-color Flag still continued to be used by locals in an unofficial capacity.
From Flag of the Republic of China 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.