That's what I believe--that there were five families including the Corleones; and the Corleones referred to "the Five Families" in a generic way. Those here who believe there were five families in addition to the Corleones can cite many examples in which the context unmistakably leads to that conclusion. But the sixth familiy, if there was one, is never named, either in the book or the film. The Bocchiccios were a New York area family, but they weren't players on the scale of the other families. They're never mentioned in the film; and in the novel, their only role in the Dons' Convention was to supply hostages to assure the safety of participants.