Revealing mistake: When Bela Lugosi walks off screen, it's obviously a freeze frame. The swaying tree stops moving and even though he was hit by a car, his shadow is still visible. (00:07:55)
Revealing mistake: In the shooting scene in the Mount Rushmore cafe, a boy in the background puts his fingers in his ears, because he knows the gun is about to be shot.
Continuity mistake: It is supposed to be night when Joe slips out of the hotel, but a daytime sky is visible.
Factual error: As Frederick is explaining to his guests how to use their .45 automatics, he fires one round at a near-by vase, shattering it. However, it leaves no bullet hole in the wall directly behind the vase.
Factual error: Anne Frank received her diary on her birthday, and started writing on it 1 month before she went into hiding. In the movie however, she is presented with the diary on the first she arrives at the hiding place.
Suggested correction: Since this movie is based on actual events and not considered a documentary, then the film-makers are allowed to change things to their liking.
While I feel like this sort-of correction could apply to certain elements of movies based on true stories like dramatized scenes (since there has to be some condensation of time and some elements boosted for drama, which can be chalked up to filmmakers changing things), I think a film based on a true story contradicting a known hard fact like this should 100% count as a mistake. Otherwise, you could just as easily argue that any factual error in any film is invalid because the filmmakers are "allowed to change it."
Factual error: The movie is set in Cardiff but the Transporter Bridge seen at the beginning of the film is really in Newport.
Continuity mistake: The doctor just killed Mr. Fleming. Cut to Agnes Moorehead playing cards; She is casting no shadow on the desk from the side view, but in the view with the camera in front of her, she is projecting a shadow. (00:11:35)
Continuity mistake: When Richard Hannay jumps from the Sheriff's window into a passing truck it is full of bales of hay. The next time we see him in the truck it is full of sheep and the bales of hay have vanished.
Other mistake: A police officer fires two shots, hitting a bank robber in the back. The "bullets" do not make holes in the robber's coat. All they do is create two tiny puffs of dust.
Other mistake: After the intro, one girl in the bar peeks from the window and goes; "Say, here comes Gordy and Jennie." And indeed the duo is getting off the car and joins them. The problem is, the window is on the opposite side of the entrance and there's diegetic music playing throughout the scene. In other words, she saw them parking to the left, but in a split second they are coming through a door on the right. (00:02:40)