I'm sure the "five or six families question" must have been asked at least once. That would have been by Coppolla. The screenplay pretty decisively made the Corleones one of five and only five New York families.

It well could have been asked at some point, but the great majority of people who interviewed him would have either given the book one quick read, or else read it after seeing the movie, and so they never really considered six families.

I did hear Puzo talk about the Mafia in Sicily being a source for his stories. I've thought the Bocchicchio might have been a way for him to introduce some of that information.