Continuity mistake: When Mary and Vincent sit in a café and Mary asks him if he is going to keep an eye on her his hair sometimes falls over his forehead, sometimes not. (00:52:20)
Factual error: In the parade scene with Joey Zasa, they are having a raffle where they can win a Cadillac Eldorado. On the car a sign reads "Win THIS 1979 CADILLAC Diesel." The mistake: This a not a 1979 Cadillac Eldorado, it's a 1980 Cadillac Eldorado. The difference is the grill and a light under the headlights. The grill for the 1979 model has 14 spaces between the vertical metal beams, the 1980 model has 18 spaces between the vertical metal beams. Also the 1980 model has orange lights under the headlights, 1979 model has no such colour. Even though these two models are almost identical, there is a small difference in appearance. (01:17:55)
Continuity mistake: When Altobello asks a young boy in Sicily to imitate a donkey, he is served a jar of wine with the handle pointing to the left side. In the close-up it points to the right side.
Continuity mistake: During the scene that takes place at the party were Connie is singing the song about the instruments, Vincent Mancini and his mother can be seen arriving to find out their names have not been listed to attend. The shot switches back to Connie singing, and Vincent's mother can be seen at a table enjoying the song and festivities. It then cuts back to the entry hall where Vincent begins to shove people around, and his mom is still standing there looking upset that they have not been admitted to the affair.
Revealing mistake: Several newspaper spins show Michael Corleone in the headline, but a screen shot reveals body copy that is unrelated or outdated. For example, the headline dated 1979 has copy referring to events occurring in the 1990's. Another has body copy with instructions from a software manual.
Factual error: When Keinszig (Swiss banker) gets killed, they knock over a pile of money including US dollars. They show US $100 bills with one problem - Ulysses S. Grant is on them. Benjamin Franklin should appear on the $100 bill. Grant is on the $50 bill. (02:28:45)
Continuity mistake: At Michael's celebration there is a scene of a family photograph taken on the stairs of his home. When the photographer is taking the picture of the family, you can see that the camera he is using is a Sinar P1. But when the scene's angle is reversed, you see the front of the camera, and it is a completely different one - a Toyo-View G.
Other mistake: In the Mafia World, Vincent would have never been appointed boss of a family without first being initiated as a full member of Cosa Nostra, working his way up the ladder from soldier to Capo, etc. As far as we know, Vincent, from the beginning, was only an associate working for Joey Zasa, then starts tagging alongside Michael, who gives him control of the Corleone Family later, after his failing health.
Other mistake: In the mafia world of Cosa Nostra, anyone that puts their hands on a made member, especially a low-level associate such as Vincent, would be immediately killed. Vincent would not have been allowed to live for viciously assaulting a mafia Capo, as was the rank of Joey Zasa in the film. Not even Michael could have saved him from such a fate had this been true.
Factual error: The opening scene shows the 1979 NYC skyline with the World Financial Center (now known as Brookfield Place) visible, which wasn't built at that time.
Chosen answer: He'd been stealing from the Family.
Captain Defenestrator