The story takes place in 1863, during The Civil War. Just before the horse stampede through town a character says, "...they'll think they're riding into Custer's Last Stand." Custer's Last Stand happened in 1876.
Uncle Willie refers to Clanton as a 'Santa Claus' when he partially reimburses the depositor's stolen money. The modern conception of Santa Claus, which eclipsed earlier incarnations and names, began with Thomas Nast's first cartoons in 1864, one year before the story takes place in 1863.
Uncle Willie carries the bag of gold in his right hand to give to the head of the bandits, Jack Lester; when the bandits initially confront him he is still holding the bag of gold in his right hand. Suddenly, Uncle Willie is hiding the gold under his left arm beneath his jacket, the same place he had put it back in the bank when it was handed to him.