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: The movie concludes with George Peppard crashing a test monoplane. The shot is from James Mason's office, looking out over the airfield. We hear the sound of the diving plane, but do not see it. After the camera has been focused on the field for a few seconds, we see a large explosion, which is meant to represent the crashing plane. The falling plane is missing. From the position of the shot, we should have seen the crashing plane. (00:12:15)
Other mistake: Robin yells "Holy Polaris" before the rocket even breaks the surface of the water.