The scene where Arkansas Dave Rudabaugh (Christian Slater) puts a knife through Chavez' arm was added due to Lou Diamond Phillips' breaking his arm during filming.
No one got away from the ambush by Garrett's posse at Stinking Springs. A few were injured, and Charlie Bowdre died. The Kid and his gang surrendered and were all taken to jail in Santa Fe, but Dave Rudabaugh eventually escaped and did flee to Mexico. Despite claims that he fled to Montana and led a "normal life", it is accepted that Rudabaugh killed two men in Mexico and was shortly thereafter beheaded. The Mexican government even took a picture of his severed head as proof that they had executed the outlaw.
During his escape from jail, Billy (Emilio Estevez) shouts out "Hello, Bob" before shooting Bob Ollinger (Leon Rippy) - the exact same dialogue that the real Billy the Kid used during the incident.
Lou Diamond Phillips (Chavez) was dragged by a spooked horse when filming a new scene. He broke his arm and a kneecap. The horse was spooked when Emilio Estevez (Billy) fired a gun and threw Lou off. The horse then ran, dragging Lou by the noose around Lou's neck and tied to the saddle horn. The scene was never re-filmed. Lou talks about this incident on Celebrity Close Calls (2010).
Emilio Estevez (Billy) originally approached Jon Bon Jovi to ask him for permission to include the song "Wanted Dead Or Alive" on the soundtrack. Bon Jovi didn't feel the songs lyrics were appropriate; however, he was inspired by the project and resolved to write a new song for the film that would be more in keeping with the period and setting. He quickly wrote the song "Blaze of Glory", and performed it on acoustic guitar in the New Mexico desert for Estevez and John Fusco.