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. (02:55:29)
Suggested correction: I've just watched this scene; there's no car visible. There's a bit where Blondie prepares his gun prior to aiming, then the camera switches back to Tuco. To the right of Tuco, in the background, a blurry something can be seen for maybe a second moving right to left. The object is far too blurry to identify. There's no reason to believe it's a car. It makes more sense that it's a horse-drawn wagon.
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)