Continuity mistake: In the scene when Billy is shooting Doc's handcuffs, Billy's revolver changes several times, shot by shot. Watch for the front sight to appear and disappear between the POV Doc shot and the medium distance shot, and for the entire finish of the gun to change at least twice.
Continuity mistake: After getting shot in the leg, not only does the Billy The Kid remain upright, but Billy is dancing on the leg seconds later.
Continuity mistake: Late in the movie, Billy is captured and jailed in an upstairs room with Bell to guard him. A knock sounds at the door and Bill raises his rifle (cocked) and points it at the door. The door is opened revealing a lady. Bell, still aiming the rifle (now suddenly uncocked), quickly lowers it.
Continuity mistake: In the first part of the movie there is a scene where Billy rides into Old Fort Sumner with the gang. He then goes into a building and meets a guy named Beaver. When Beaver is first talking to Billy he is wearing an eye patch over his left eye. A minute later he is seen talking to Billy (about the soldiers coming and harassing him) and the eye patch has mysteriously disappeared.
Continuity mistake: When Dave stabs Chavez in the arm the blade gets stuck in his arm. It is pointing up in the air when this first occurs. When Dave later pulls the blade out of Chavez's arm, the blade is pointing down towards the ground.
Continuity mistake: After Billy shoots all the candles, there is still a reflection of one burning candle. The window is also open before and after the shooting, but is closed during, seen in one closeup. (00:22:35)
Continuity mistake: During the scene at White Oaks, it is a different door when they are inside the house compared to the door when they are outside. One side has the glass at the door knob, the other side it's 3/4 the way down the door.
Answer: Doc says in the movie he is married with kids. So you have to assume he married her.