Continuity mistake: When they pick up Warren on the stagecoach, the second shot from inside has the wrong direction of landscape outside, so it seems that Warren changed from the front to the back row.
Revealing mistake: When Warren begins shooting Bob, a massive blood spurt is shown each time he shoots him. Each time he is shot, the blood spurts don't line up with the area where Warren shoots at. The first time Warren shoots Bob, the gun is showing firing at his stomach, but the blood is shown spurting from his chest and the second time he shoots Bob, the gun is fired at the top of his chest, but the blood spurts come from a couple of inches below where he was shot. (01:57:00)
Factual error: Six-Horse Judy has a distinctive New Zealand accent. But the New Zealand accent would not have been in existence as early as the period in which the movie is set. The non-Maori inhabitants of 1860s/1870s Auckland were largely British or Irish settlers who would have spoken with the accents of their native countries, as would their New Zealand born children.
Continuity mistake: After Warren (Samuel L. Jackson) asks everybody to stand against the wall, he orders them to throw away the snowshoes hanging there. They throw them right to the front of the fireplace. In the next shot Warren takes some steps ahead and the snowshoes are in the background: they changed their position. (01:46:00 - 01:47:00)
Factual error: When the criminal gang arrives at the Haberdashery and kills Minnie, Six-Horse Judy, et al, there is blood everywhere, including big smears on the floor. In the 1860's/70's, it would have been virtually impossible to clean up all that blood, especially on wood plank floors, but when the second stagecoach arrives carrying Major Warren, John Ruth, Daisy and Chris Mannix they don't notice that a massacre just occurred there. Even today, with much better cleaning tools and solutions, it would be hard.
Continuity mistake: In the scene after they pick up Mannix in the stagecoach, Warren has his gun pointed at him because they don't trust him. Warren is somewhat relaxed with his arms crossed while keeping the gun pointed toward Mannix, but in the next shot he is right up in his face with the gun, and in the next shot he's relaxed again.
Other mistake: In the beginning of the film when the stage coach is approaching Minnie's haberdashery, a well-worn horse path when approaching the haberdashery but it's been snowing a long time, and there is not a lot of traffic going to the haberdashery so this path should not be so worn.