I managed to get a hold of the 4-DVD box "The Godfather - The Coppola Restoration", apparently from 2009, with all three films plus a bonus DVD (
everyone does appendices by now, don't they? 😁), in a German version (so at least original and German synchronization). Seems it was a last-ditch rescue mission, as especially the celluloid copies of the first two films were disintegrating.
I also know that my parents had Mario Puzo's book in their big living room bookshelf, and that I read it - before the first film came out, I'd guess, as I recalled the "
horse's head" scene to have been different in the book.
But then, besides
Coppola directing all three films, just look at the actors who were involved:
Brando, Pacino, Caan, Duvall, Keaton, Hayden,
Shire in part 1
Pacino, Duvall, Keaton, De Niro, Shire, Strasberg in part 2
Pacino, Keaton, Shire, Garcia, Wallach, Hamilton, Berger in part 3
And dozens I didn't mention above. These were different from the Agathe Christie-derived "Hercule Poirot" films of about the same time, starring Ustinov or Finney, or the disaster films also so popular, which had a huge cast of recognizable names in their credits - some of which were a bit past their screen prime.