[tomp]

Interesting that Slovenia and Yugoslavia are reported as separate countries (with suspiciously close switching dates). Technically, in 1919 neither country existed - what is now Slovenia was a constituent of Kingdom of Serbs, Croats and Slovenes, which was renamed to Kingdom of Yugoslavia in 1929.

[Aqwis]

I wonder if Slovenia did really not switch before 1919. It was part of the same "country" as what are now Austria and the Czech Republic for hundreds for years before that, who according to the list switched in the 16th century.

It seems unlikely that what is now Slovenia would use a different calendar than the rest of the Habsburg Monarchy/Austrian Empire for such a long time, particularly since there was no subdivision of the Empire that directly corresponds to modern Slovenia.

[mantas]

It's interesting that Lithuania and Poland have different dates too. Poland and Lithuania were a union back in 1582 and the change was made throughout the Commonwealth. It was switched back during Russian occupation in 19th century though. Both in Lithuania and Poland switched to Gregorian again after WWI.