Greece is gone

[TNZ]

I'm playing as Russia, and I just conquered a handful of provinces off the Ottomans in Greece, with Greek culture, to release a vassal: Greece.

But to my surprise I don't see the option in my release vassal list. There is no Greece, nor a Byzantium in case you wonder. When I check the provinces, there is no Greek nor Byzantine core, even if the culture is Greek, and the religion is Orthodox.

I vaguely remember an event that gave me Russian permanent claims on Greece, is that the reason the Greek cores have disappeared?

[Omniconda]

cores can disappear over time if its incorrect culture, and they are not contested for 50 years, Constantinople is turned to Turkish when ottomans move their capital and they may culture convert other provinces away from greek later.

[Landbanana]

Cores automatically go away if their country no longer controls the province after 150 years. So, if it's after about 1600 in your game then the cores would have most likely run out.

[Azazel]

there is a event bout greek seperatism i think in the 16somthings where greek "gets "their cores

[Arcrom21]

Greece cores will only appear more later via event (can't remmember the date) but greek rebels can still spawn and create a core if they siege a greek culture province.