Poland was occupied by Germany during WWII. The people still considered themselves Poles during this time, and the only reason there wasn't a 'Poland' was because of military strength, so it seems silly to say that early 1939 Poland and late 1944 Poland are different countries because of lack of continuity. Certainly, almost all Poles will tell you the country 'began' (it kind of had a soft start) in 966, and not in 1944.

(Note: there was technically the government-in-exile in London, which you could argue maintained continuity, but I don't think it's necessary so I'm leaving that out of this.)