When the final shootout starts, Stagecoach Mary disappears and is never seen again.
The 'gingham' apron isn't gingham.
Nylon bristle toothbrushes weren't invented until 1938.
Pickup trucks and equipment visible in stagecoach window
When Mary shoots the chicken leg out of Graham's hand, the string pulling it back is visible.
The first night Isaiah was with the Spaniard, several crew members can be seen around their bodies.