premise: Bernardo Provenzano (] ; 31 January 1933 – 13 July 2016) was a member of the Sicilian Mafia ("Cosa Nostra") and was suspected of having been the head of the Corleonesi, a Mafia faction that originated in the town of Corleone, and de facto "capo di tutti capi" (boss of all bosses) of the entire Sicilian Mafia until his arrest in 2006.
hypothesis: It was never confirmed that Bernardo Provenzano was the leader of the Corleonesi. 
reason: Provenzano was only suspected as the leader of the mafia. It wasn't confirmed.