Factual error: In the scene where all the heads of families meet shortly after Sonny's death, there is an exterior shot of a large grey-brick building with an American flag hanging from it. If you look carefully, the flag is a current flag with 50 stars, with alternating rows of indented stars. But, the scene is takes place circa late 1940's when there were only 48 states and all the rows of stars were even. (By the way, the flag inside the meeting room is the correct one.) (02:01:05)
Factual error: The Cadillac Miller and Cadillac Meteor flower cars at Vito Corleone's funeral are an anachronistic impossibility, given that he died some time in the summer of 1955. With two exceptions (one from 1951 and one from 1955), the Cadillacs serving as flower cars are 1956 models. Although a 1956 Cadillac Fleetwood 75 limousine also makes an appearance, it's plausible that the funeral could be taking place at a time when the first 1956 Fleetwood 75's were released. Miller and Meteor, however, did not begin converting 1956 Cadillacs into flower cars until 1956 proper.
Factual error: On the way to the meeting when Michael is going to kill Solozzo, the car made a U-turn on the George Washington Bridge (GWB), which connects Manhattan to New Jersey. However, the scene is shot on the Queensborough (59th Street) Bridge, which connects Manhattan to Queens. They look nothing alike, the GWB is a suspension bridge, the Queensborough Bridge is a cantilever bridge. (01:22:35)
Factual error: At the end of the movie, when Michael's car pulls up in front of the Las Vegas hotel, if you look through the glass windows, two men wearing 1970's shirts and gold neck chains, with "hippie-style" haircuts walking through the lobby, though this is supposed to be in the late 40's or early 50's. (02:13:50)
Factual error: When Luca Brasi goes to meet the Tattaglia family and Sollozzo to pretend he would like to defect, and they garrote him, Brasi is making all kinds of loud noises while being strangled until he dies. During choking or strangulation, one is unable to make much (if any) sound because air cannot pass through the vocal chords on its way out of the body just as it cannot enter the body and get to the lungs. (00:41:25)
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.
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.