Well, if we really want to get into inconsistencies on that date: Vito's birthdate, accoding to his tombstone in GF, was April 29, 1887. How'd it get moved to Dec. 7 in the flashback scene?
Clearly Part 1 and Part 2 had different timelines. Part 2 had Vito's age as nine when he came to America in 1901; that just doesn't agree with his tombstone in Part 1.
FFC usually is pretty good with details like these but I guess even he couldn't imagine the scrutiny these things would be getting so many years after the movies were made.
