Other mistake: In the very last scene of the movie, and just before Blondie shoots the rope that is holding Tuco on the grave's cross. You can see a car moving in the background, screen right of Tuco's head.
Other mistake: Johnny Finger is supposed to be a crack shot, and in his first scene he supposedly beats three guys on the draw simultaneously. However, as he goes for his revolver with his left hand, it goes off almost immediately whilst still pointing straight downwards. (00:02:45)