Other mistake: During the driving scene in the woods with the Bronco, at least two shots are reused twice.
Continuity mistake: The movie opens with an American Football match; look out for the girl wearing number 6 for the red team, Molosses, who has mid-length locks of straight reddish hair coming out of the helmet, down her back. When a touchdown is scored and celebrations begin, number 6 takes her helmet off, revealing the face of the protagonist, Karidja Touré, who has long black hair in braids. (00:01:20 - 00:02:40)
Continuity mistake: When Elizabeth Banks is getting out of Amos' car, when they get back from Bible study, from Banks' angle, you can see that his hand is on the knob on the steering wheel, whereas when the camera changes to Amos' angle, he isn't touching the knob. When the camera changes back to Banks, you can see his hand back on the knob. (00:48:10)
Factual error: As the marchers start through the streets before they gather at the Edmund Pettis Bridge, they pass by a shop with a Pepsi sign. The Pepsi logo, however, is from the 1980s-1990s.
Factual error: During the Hungnam evacuation scene in December 1950, a U.S. Army Captain is using a radio handset. The model he uses is the H-250, which was introduced in 1987, over 30 years after the Korean War.
Continuity mistake: Carrie's height changes constantly.
Factual error: When the Germans come to the town a tank rolls through the picture. The first shot shows the tracks, then the whole tank is shown and one can see the tracks again. The turret suggests a Panzer III (which would be accurate for the time). It appears however that the tank is a modified Russian T34 or T55 or something as the road wheels are too big for a Panzer III. (00:13:00)
Factual error: In the opening scenes where Margaret drives to San Francisco, her car is an early 50s Meteor. Meteors were a Ford Motor Company brand just above Ford (a bit like Mercury) but were sold only in Canada. Meteors often were only rebadged Fords, like this early 50s model. The rest of 50s and 60s car choices in the film seemed perfect.
Character mistake: When Jesperson imagines himself as a Mountie his uniform is completely wrong and is not even the right colour. As it was his ambition to join the force and he has photos of RCMP officers in his cab, it seems unlikely that he would imagine himself in a completely incorrect uniform.
Suggested correction: It's not a character mistake, for the reasons stated; it's a clear factual error from the filmmakers.
It's a character mistake since it's his imagination and, as you stated, it's not something the character would get wrong.
Continuity mistake: Kevin Shepherd pulls over in front of her fiancee's dad. It's still a wide angle, but you can see distinctly both her and his left arm stretched forward; she is looking at her engagement ring, he has his hand on the steering wheel. Before the camera cuts away though, he lowers his arm; it is not acknowledged in the new shot, where both have still their left arm forward. (00:03:35)