I have never seen YYYY-DD-MM format, on the other hand, both DD/MM/YY and MM/DD/YY are equally common, that's why I always prefer YYYY-MM-DD format as it is the least ambiguous and most useful (sorting files etc., as other comments have mentioned). Feel free to prove me wrong though.

I work with non-techies. Most are totally unfamiliar with YYYY-MM-DD so weren't sure what a date that was ambiguous in that format was. I totally agree that usage of YYYY-DD-MM is rare (in my experience, anyway), but none of these formats fare particularly well when it comes to discoverability.

Have you ever been to any of Kazakhstan, Latvia, Nepal or Turkmenistan? https://en.wikipedia.org/wiki/Calendar_date#Gregorian.2C_yea...

I can assure you that Latvia does not use YYYY-DD-MM. Officially Latvia is using ISO 8601. https://en.wikipedia.org/wiki/ISO_8601#Usage

I’d update the Wikipedia article but don’t have time to go digging for official sources. Something you (or someone else with domain knowledge) could do?

I've been to Latvia many times in last few years, but haven't noticed YYYY-DD-MM format, maybe it's historical? It looks like DD.MM.YYYY was the most common format there (at least on posters).

Japan and Denmark use this format.

If you have enough examples, you can see which field goes over 12. In undocumented datasets, that's the only option.

That assumes that the dataset is consistent with itself.

Well, you gotta assume something ;)

And you're right. I've seen some pretty strange stuff.

Sometimes, when forced to use ancient enterprise data systems, desperate staff use abandoned fields for new purposes.