I know, it depends on whether the churches are on Gregorian or Julian calendar.

And not everybody in ex-USSR were on the old calendar.

Who wasn't? I guess Cechnya?

Estonia/Latvia/Lithuania and other catholic and protestant communities.

There's quite a few Uniates on the old calendar, though.

Yes. But Lithuanian and Latvian are Catholics are Roman and protestants in all three are on new calendar (not sure if any protestants use old calendar at all?). And not all catholics outside of baltic states were unites. E.g. western Belarus and western Ukraine has some Roman Catholics. IIRC there’re some Roman Catholic islands inside RF too, but they are tiny. Probably mostly artifacts of forced resettling in Soviet or tsarist eras.

Greek Catholic and for the first time Ukraine.

I understand Ukrainians celebrate Christmas officially now for the first time.

(If I understand correctly last year it was some kind of transition.)

They did celebrate it before, but on January 7th (which on Julian calendar is December 25th, because it lags 14 days). This year their Orthodox church switched to Gregorian calendar.

Yes, agree.

Sorry for the confusion, "now" in my comment above was ment to refer to the current time, i.e. the 26. or 27. (or whenever I wrote that comment).