Continuity: After he kills Alamosa, Billy mounts his horse and passes by Alamosa's body. Then the body is in a different position.
Continuity: When Cody is lying on a bed, his left arm is over the rifle, with his hand hanging from the bed, and his right hand is leaning on his left shoulder. In the next shot, when Poe touches him, his left hand is holding the rifle and his right hand leaning on the bed.
Anachronisms: Though the film takes place in 1881, many of the characters use Winchester Model 1892 rifles which were not available until 1892.
Factual errors: Lemuel refers to Pat Garrett as "Patrick J. Garrett." But Garrett's real middle name was Floyd.
Crew or equipment visible: (At 36:00) During the Governor's interview with Pat Garrett at the dining table, the shadow of the boom operator is clearly visible on the table cloth to the right of the Governor.
Errors made by characters (possibly deliberate errors by the filmmakers): Sheriff Pat Garrett stands up and props his back against a tree to aim his rifle at the old man on the river raft (the man is also aiming at Garrett). By placing himself completely out in the open like this, Garrett makes himself a perfect target for the other rifleman, who luckily does not fire. A real sheriff would have positioned himself BEHIND the tree for maximum protection and concealment.
Revealing mistakes: Richard Jaeckel (Sheriff McKinney) wears a very obvious wig in all his scenes.
Factual errors: In 1881, while Pat Garrett and his posse are shooting at Billy and his gang, who are holed up in a remote stone building, Garrett calls to Billy and says that he is wanted for the killing of Buckshot Roberts. Billy yells back that the Roberts shooting had taken place a year ago. In fact, Roberts was shot and killed in 1878 - three years earlier - by Charley Bowdre, another member of Billy's gang.