Yup: as IMDb has the best database, it has this documentary that was among the bonus disk of the collector set and so I had to review it!
As I saw it after the other extras, I was already satisfied. There are interesting tidbits with personal interviews of Coppola, Pacino and even De Niro but the editing is awful: the sequences aren't organized but merely added one after another and all the three movies are finally mixed together.
Worse, nearly all previews of the movies have a horrible quality.
What I retain is that the studio executives really don't understand what movies are about: I wonder what happened to the ones in Paramount who wanted this movie with no Coppola, no Brando, no pacino! It was clear as water that to do a movie about cosa nostra, it had to involve italo- Americans and not wasp.