I am really surprised that with all the Godfather books being written that no one has tackled a post-part III book yet. The Winegardner and Falco books all seem to be about the golden years, which is understandable, but I think there is enough material based on notes FFC and Puzo perhaps shared when part IV was being discussed to base a novel on. Of course you'd have to get the approval of FFC and Paramount, most likely, to be able to use info from the movies, but it's only gonna make them more money, so I think they'd approve.