Continuity mistake: Bond sits down by a table, puts some cards down and pulls his gun out. He's wearing a tie, but when we see a close-up of him screwing on the silencer, his tie disappears. (00:54:40)
Factual error: A poster promoting the July 4th fireworks spectacle includes an illustration of two American flags - each with 50 stars, rather than the 48 stars which they should have at the time. (00:46:40)
Other mistake: In the opening credits, there is one credit that reads "Miss Winter's costumes by Gene Coffin." This is meant to be referring to actress Shelley Winters and the man who provided her costumes, however the apostrophe has been put in the wrong place. Since her full surname is Winters, putting the apostrophe in between the R and S in incorrect. The apostrophe should have gone after the S to spell out "Miss Winters' costumes" and not Winter's. (00:01:35)
Continuity mistake: During the election meeting held at the saloon, there's a large sign that reads "Capitol City Here We Come" on the wall by the stairs. We see this sign in numerous shots. When Valance enters the saloon there's still a sign on that wall by the stairs, but now the painted handwriting on this sign is different. Moreover, the original sign that had been by the stairs is now up on the side wall of the saloon, where Valance and his thugs stand; note the handwriting. (01:09:20 - 01:13:45)