Other mistake: When in the tub in Arkansas, Wyatt is bare chested. In bed with Josie he's suddenly sprouted a lush garden of chest hair.
Factual error: Throughout the entire film the wrong holsters are used. They are wearing "drop loop" holsters but they weren't invented until the 1930s.
Factual error: During a shootout at the end of the movie, one of the gunmen with a rifle is wearing a wristwatch. (02:00:00)
Factual error: The movie begins at the end of the Civil War, 1865; it then moves ahead 7 years, to 1872 in Wyoming. Several characters are wearing gun belts with cartridges on the belt. The pistols are Colt Peacemakers probably .45 cal. The problem is that the gun and cartridge were not introduced until 1873 and would take several years to become commonplace.
Continuity mistake: When Morgan is shot while playing pool he is placed on the pool table. An overhead shot shows a wide pool of blood spreading from his right side. In a subsequent shot the pool of blood is much narrower and a completely different shape.
Continuity mistake: When Wyatt meets Doc for the first time, the amount of liquid left in Doc's drink keeps changing.
Revealing mistake: During the bison shooting scene, a bison goes down close to the camera and both horns jiggle like they're about to fall off. Looks quite fake.
Continuity mistake: When Doc confronts Ike looking to fight there are a lot of people around. Then from the camera angle from behind Wyatt there is no-one around.
Continuity mistake: When Wyatt is confronted by Ed Ross in the bar after refereeing the boxing match toward the beginning of the movie, he has a pistol in his belt when throws the cue ball at Ross. Wyatt still has the pistol in his belt when he takes Ross' gun and holster and straps them on. But when he and Sally walk outside right after, the pistol that was in his belt is gone.