When William Holden ambushes the stagecoach robbers he removes the leaders gun from his holster two seconds later he is seen removing it again.
In the early rounds of the fight, Dutch gives Dan "Texas" Thomas a large bruise on the side of Dan's face near his left eye. However, at round 35, the bruise no longer shows in a closeup of Dan. Then the exactly sized bruise is back on Dan's face in the same place at round 40.
The story set in 1866, post-Civil War Texas has everyone armed with Colt Model 1873 pistols with bullet loops full of cartridges on their gun-belts, even the movie poster has William Holden's character Dan holding a short barrel 'gunfighter's' version of the .45 caliber pistol. This is seven years before the pistol was introduced by Colt. The most common sidearm of the day would have been the Colt 1869 Army which was a cap and ball weapon that had to be hand loaded chamber by chamber with powder, wadding and a ball projectile.
Claire Trevor's hairstyle is strictly 1941, even though the story is taking place in 1866.