Other mistake: There's a minor technical error in the portrayal of the telegraph equipment at the train station. When a message was coming in for the stationmaster the repeater relay, on the left, was shown clicking away. The telegraph sounder to the right wasn't moving. Both should have been in use as the repeater relay would have been fairly quiet while the sounder would have created the loud audible clicks. Repeater relays with fresh sets of batteries permitted the telegraph signal to travel greater distances by regenerating the Morse code signal at each telegraph office. The sounder made it much more audible. An office at the very end of a telegraph line would only have a sounder.
Other mistake: Before the trial by combat, when Richard Taylor and George Sanders choose their weapons, they are brought to them on their shields. But this happens to quickly, right after the choices were announced, as if predetermined.
Other mistake: Maureen O'Hara's brother punches John Wayne. You can tell how far away from him Wayne is, and the sound of the punch is a touch off. He's punching air.