Other mistake: Brian Keith sneaks into an Indian encampment at night while they are sleeping. In order to stampede their horses, he rapidly fires the one and only six-shooter revolver he has into the air...eight times.
Other mistake: At the beginning, when Rosie strips down to bathe in the lake, only her skirt comes off, revealing her bare bottom. But not her blouse.
Other mistake: The old man is plowing the field in front of Belle's old residence. The little girl picks up the doll. A second before the cut, the girl lifts her eyes from the doll and does not look at her pops, or around; she looks right at the fourth wall and smiles, waiting for her cue. (00:01:50)
Other mistake: While Ransom Stoddard and his wife are on the train back to Washington, the conductor tells them that the train will be able to maintain a speed of 25 mph throughout the journey. The film is set around 1900, by which time trains were regularly topping 65 mph, and the outside scenery is moving faster than it would for something traveling at 25 mph.
Other mistake: Just as the preacher finishes stitching up Jake's wound, a shot rings out from the street, and everyone goes outside to find Percy Dollarhyde drunk and shooting up the town. Percy is right-handed but holsters his 6-shooter revolver on the left, and this appears to be his only sidearm. Even if he did carry another 6-shooter, that wouldn't explain how he fires 13 shots in this scene without reloading.
Other mistake: The villain's plan is to impersonate along with his large crew a platoon of the Mexican army. He already captured the soldiers and has them incapacitated, all he needs to do is take their uniforms. Instead of doing so, though, he mows down the whole lot with a heavy machinegun. When it's time to put on the show, everyone wears nice and tidy white uniforms.
Other mistake: Just after newlyweds Gil and Lana arrive at Gil's small log cabin, they are visited by a Native American named Blue Back, who brings them a side of venison. Even though it has been pouring rain outside for hours, Blue Back is perfectly dry when he enters the cabin.
Other mistake: Jed has eight rounds on him/in his pistol. He tells Chad to go to his saddlebag to get another round of ammo and keep it in his pocket. Jed tells Chad "Let's play catch the bullet" since Chad (not his marshal dad Britt) is the only MacMasters there. Jed fires six rounds before Britt shows up on top of the hill, then two more (eight rounds). Jed shoots a ninth and tenth round before he tells Chad, "Get that ammo." Chad is never shown giving Jed the ammo from his pocket, but Jed keeps shooting. (01:13:42 - 01:17:46)
Other mistake: John Wayne is recruiting other victims of outlaw violence to assemble his Avengers team; he gives them handwritten notes saying, "Go to Hall's barn at ten o'clock tonight." Forgetting the fact that he somehow managed to find a dozen or more ace gunslingers with his same vengeance agenda in the vicinity of the same barn, it is obvious, looking at the two handwritten notes, that they were in fact written by very different hands, not by just one person. (00:12:50 - 00:13:25)
Other mistake: Captain Stanley takes the lid off a small bottle on his right and puts the lid on the desk. He pours a drink and the lid miraculously appears in his left hand. He then screws it on the bottle. Screw top bottles weren't around till 1920. (00:54:50)
Other mistake: Handsome and Charming head out of Snakes End (followed by the newlyweds) and begin their long journey. It then cuts to Cactus Jack before he begins the journey, and at the start of this shot as he places Whiskey's bit, we can see the signpost with three wooden arrow signs and the hillside behind him. This is the same location where Cactus Jack lays trap number seven, named "the tunnel in the hillside," on the next day during the journey; noticeable when Handsome and Charming arrive. (00:28:35 - 00:54:45)
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.