In the scene where the gang is surround by Garrett's men and Doc is shot, Arkansas Dave Rudabaugh is seen standing straight against the wall holding both guns up, after Billy hands Doc a second gun, Arkansas Dave Rudabaugh can be seen crouched with the right hand gun parallel to his side. In the next shot he is standing against the wall again with the guns held up.
When the gang is surrounded by Garrett's men, Billy cocked same gun two times. First time when he pointed it toward Dave, and second time just a second before Doc ran outside.
When Billy first enters Beever Smith's establishment Beever is shown as having an eye patch. As they go to the next room Beever no longer has the patch, nor does he wear one the rest of the scene.
After his capture, when Billy is in the room with Deputy Bell, there is a knock on the door, Deputy Bell cocks his Winchester, putting the hammer back in the firing position. When the door opens, the Madam, Jane Greathouse, is standing there, Bell has the Winchester at his shoulder and the hammer is in the down, or fired position.
When the Kid is going to shoot thought Doc's chain in some angles the front sight of the Kid's revolver is filed off, in some it is intact.
Pat Garrett did not begin work on "The Authentic Life of Billy, The Kid" til 1882, long after he had shot Billy.
Marshall Ashmun Upson did not ride with Garrett in the pursuit of Billy the Kid. Garrett would not even approach Upson about writing their book till after Billy was dead.
As the much older Billy The Kid is narrating over the scene where Deputy James Carlisle is murdered, he claims that they pinned that murder on him too, but he never fired one shot. Actually, he is the very one that fired the first shot over the deputy's head, in order to draw their fire into the deputy that killed him. So actually, that murder is indirectly his fault too.
When Arkansas Dave and Chavez fight over the burial ground, Chavez is laying on his back with his arm up and Dave stabs him through the back of his arm. When Chavez asks if he wants his knife back, they are both standing up and Dave pulls the knife out from the opposite site of the knife entrance.
When Billy and the gang are talking to John Chisum the actor playing him, James Coburn, has a generous application of fake tan on his face (This is common in Hollywood and done to make older actors look younger). As the wind is in his face his hair is blown back and you can clearly see his normal skin color and the fake tan 'line'.
When Billy writes on the wall in blood he misspells Garrett (using only one t) in "Garrets Place"
In the VHS release, instead of the correct 1981-1994 20th Century Fox logo, the 1953-1981 logo is used.
The Royal Albert tea cup that John Poe uses was not manufactured in that pattern (Old Country Roses), until 1962.
When Billy and his gang ride under the bat guano chute, a modern carabiner can be seen hanging from the end of the chain.
The land border between New Mexico and the nation of Mexico is a mountainous region with a few flat plains with no rivers and only tiny streams. If the gang was seeking to flee into Mexico there would have been no natural physical barriers to stop them and the crossing could be accomplished within minutes.
Shortly before Tom O'Folliard gets shot, Billy states "we'll have a clear view of the Nachita River. We'll sell the horses off, and then we'll take a skiff downriver into Mexico." There are no rivers in New Mexico, besides the Rio Grande and Pecos [Pecos flows through several hundred miles of Texas first], that flow towards Mexico, and, in fact, there is no Nachita River.
The scene at the bat guano town was quite obviously filmed at Kasha Katuwe Tent Rocks, which is not in Lincoln County (it is now in Sandoval County). In 1880, it was in Bernalillo County and Sheriff Garrett would have been about 80 miles outside of his jurisdiction, across 2 county lines.
Fort Sumner is shown to be surrounded by mountains. In reality, the area is a vast plain and there are no mountains like that anywhere near.
In the whore house scene where the towns people mistakenly shoot the sheriff, Billy explains in voice-over that he was blamed for that killing though he never even fired a shot. This is an error as Billy clearly fires the first shot as he pushes the sheriff out of the front door inciting the towns people to open fire on who they think is Chavez the Indian.
ALL of the major and minor characters have perfect teeth.Since dentistry consisted of pulling teeth and manufacturing dentures in the Old West, this would not have been possible.