When Billy the Kid teaches Rio how to shoot, Rio shoots twice at four bottles, hitting two of the bottles with two bottles left standing. However, when Rio turns around and walks away, all bottles are broken and there are none left standing.
When Billy the Kid and his gang are held up in a small shack by Pat Garrett, Billy stands on the right side of the door. Then jumps to the other side. In the next shot, one of Billy's men is already comfortably slouched in the corner from which Billy the Kid just jumped. He would not have had enough time to do that and assume that position.
Near the end when Garrett goes out to the street from the bar, his leaves his hat on the floor where it had fallen. After the final confrontation, he puts the kids on horses, and walks over to his horse and grabs his hat - which is now hanging from the saddle horn.
The hotel in Lincoln N.M. that Ollinger brought the prisoners for lunch was the "Wortley". Not the "Mariposa" as shown in the film. The "Wortley" is still in business.
Billy refers to Wallace as being elected. Lew Wallace was not elected, he was appointed as territorial governor. Also, when Pat commandeers the stagecoach he does it in the name of the state of New Mexico. It did not gain statehood til1908, more than 25 years later.
In the movie Dave Rudabaugh is hanged in Santa Fe. This is not correct. He was shot in a gunfight in Chihuahua, Mexico, in 1886.
At one point, Pat Garrett claims the authority of "the state of New Mexico". At that time, New Mexico was only a Territory.
In the final scene, when Sara (Leila George) reaches for her brother's hand, there is a very large, very modern tattoo on her wrist and forearm.