I don’t know what the post-Soviet opening of archives showed, but the CIA officially believed that an anti-Communist partisan organisation survived in the Baltic states until at least the mid-50s.
But it was also a standard Soviet counter-intelligence practice to foment counterfeit resistance organisations to flush out dissidents and snare foreign intelligence agents attempting to contact them.
So no one knows for certain how long the anti-Communist partisans lasted before they were transformed into KGB Trust operations.
Actually when I was in the Museum of Occupation (which encompasses the Soviet Occupation, the Nazi Occupation and then the Soviet Occupation up until 1990) in the Latvian capital Riga a few years back I seem to recall that even after the defeat of the anti-Communists who did indeed fight on with CIA support right into the 1950’s (and one never hears about that sort of thing in the history books) it was not until 1991 with Latvian independence that the last of the old resistors finally came out of the woods.
Kinda impressive I thought and it makes those Japanese found in Pacific islands in the 1970’s seem like pikers.