The GF story (the original Puzo novel, the movies, and even the Winegartner books) exist in a weird amalgam of reality and alternate reality.

WWII, the Cuban revolution and the death of Pope John Paul I took place in about the time they really did in real life -- but not exactly.

I believe in "Revenge", they discuss the Cuban revolution and the guy who takes over is not named Castro. Plus you have the charismatic young Irish president who is assassinated, his name is Shea, not Kennedy.