Guantanamo is leased like Hong Kong used to be, and has been since the Spanish-American war. It is an exception because the US refuses to normalize relations with Cuba. That is not the case for Ramstein and the European bases, which are generally just there by agreement which does not convey sovereignty.

Another special case is the UK sovereign bases in Cyprus, which really are UK territory; I only know about those because during Brexit they kept getting mentioned in the treaty documents.

Bonus pull out sovereignty section: to whom does Transnistria belong? How about Nagorno-Karabakh?