Masseria was not from Corleone so far as we know. Yet the Corleonesi acknowledged him as the Boss.
Something is left out.
leaving aside the specific question of why the corleonesi would defer to an outsider, there is the basic question of the "mechanism" of affiliation . . . .
that is, if there were in essence 3 main "fields" of ny mafia pre-1931, one Corleone, one Palermo, one Castellammarese, then did gangsters with ties to one of these areas "naturally" or "automatically" gravitate toward the respective field? or was the mechanism much looser?
obviously mobsters like Costello and Anastasia had nowhere to go other than to join a family from a different region than their own
but how to account for a mobster like Lucchese, born in Palermo, but a close associate of such Corleonesi figures as Gagliano, Reina, Luciano, etc?
