Factual error: When Cary Grant is attacked by the crop duster, he is supposed to be between Chicago and Indianapolis. Unfortunately, northwest Indiana looks nothing like this. The scene in the movie has miles and miles of treeless landscape. Even in the flattest farmlands of Indiana, there are many visible groves of trees.
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: In the shot where the female band members run from their hotel (in Florida) to the beach, mountains can be seen in the background.
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.
Factual error: When the military are going to attack the flying saucers in Washington D.C., there's some shots where you can see trucks and airplanes in a deserted region. Washington is hundreds of kilometers away from the desert. (00:18:30 - 00:21:10)