You're right the family was founded by people from Corleone, but that town is also in Palermo province.
As we saw with Toto Riina’s war, Corleone and the town of Palermo might as well be different planets. The former is much smaller and more rural. That being said, US mobsters might be so Americanized that they don’t give a shit (even by the time of Gambino’s reign in the sixties).
"It wasn't very good parsley to begin with, and then the cat went and peed on it." -Sicilian proverb
