Factual error: Michael had his meeting withe Solozzo around Christmas of 1945. On the way to the meeting, the car made a U-turn on the George Washington Bridge (GWB) to throw off anybody who might be following. At the time, the GWB had four traffic lanes, two in either direction. The median between the two set of lanes was about 20 feet of steel mesh, making such a maneuver impossible. The median was filled in to add two additional traffic lanes in 1946. At that time, the u-turn would have been possible.
Other mistake: As the camera pans in on Woltz's mansion right before the horse's head scene, his bedroom is on the second floor. However, the windows in his bedroom show a courtyard in the background. The horse's head scene was filmed in a dining-room-turned-bedroom at a Guggenheim mansion on Long Island. The Guggenheim dining room is located on the first floor, as shown in a February 2022 episode of Antiques Roadshow.
Factual error: In the establishing shot of the movie producer's mansion, a car in the driveway is suppose to be a 1937 Cord, but actually it is a replica produced between 1968 and 1972. Real Cord cars had bug eye headlights that cranked out of the fenders. The replicas had fixed glass covered headlights in the fenders.
Other mistake: When Michael arrives in Las Vegas at the Hotel Continental and exits the car two men are visible through the window inside the hotel who are dressed in 1972 contemporary attire, despite this being set in the 50s. The man on the left in a blue jacket looks as though he could be David Geffen. (02:19:38)
Visible crew/equipment: During the meeting between the Corleone family and Sollozzo to discuss drug dealing you can see a boom microphone reflected in the glass window when Don Corleone stands up to pour Sollozzo a drink, it can be seen moving around. A little later in the same scene when Don rejects Sollozzo's offer you can see a crew member reflected in the same set of window's moving around (above Sonny's head). (00:37:20 - 00:38:44)
Continuity mistake: When Michael is sitting with Sollozzo and McCluskey, the owner (presumed owner) of the restaurant (shown from the rear, walks behind the bar to ring up and put a check in the register, he is smoking a pipe. (in his mouth) But yet a split-second later from a front angle there is no pipe in his mouth, hand, or anywhere near him.
Continuity mistake: When Tom is walking down the alley between buildings at Woltz Studios before he meets Mr. Woltz, the bag he is carrying looks like a travel bag and is almost equilateral triangle shaped. When he meets Mr, Woltz, his bag is a much thinner (isosceles triangle) shaped briefcase. In almost every shot the hand carrying the "bag" is switched. (00:27:45)
Audio problem: When Vito Corleone is brought back from the hospital and he is upstairs in his bedroom with his other family members, after his grandson Frank gives him his gift, the baby who was just crying has his mouth completely closed while the audio has him still crying as they leave the room. (01:33:00)