Factual error: At the beginning of the movie, in the conversation betwenn Frank James and Robert Ford, the term "gunslinger" is used a few times. However, the term "gunslinger" didn't come into use until the 1920s (the movie is set in the 1880s).
Factual error: After the opening narration, the action continues to the food kettle, indicating supper time, as the men gather around Jesse. On a close shot, one of his cohorts is smoking what appears to be a perfectly round, lit cigarette. Filtered cigarettes were not introduced until about 1894. The non-filtered were introduced only 2 yrs prior. This film is based in 1881.
Continuity mistake: During the conversation between Jesse James and Charley Ford after James has killed Ed Miller and woke Charley in the middle of the night, Charley's right suspender is initially twisted, yet, in the next shot his suspender is flat against his body, and remains so for the rest of the sequence.
Other mistake: During the film the narrator states: "He also had a condition that was referred to as "granulated eyelids" and it caused him to blink more than usual as if he found creation slightly more than he could accept." However, this never occurs once in the movie and in fact the opposite happens, Jesse stares into space hardly blinking throughout the entire film.
Continuity mistake: While Dick Liddle is talking to Robert Ford, Ford's hair is curled to his left, yet in one shot during the sequence, Ford's hair is straight, then goes back to being curled the rest of the sequence.