Middleton is singing and playing the guitar as he approaches the town. When he goes off to Mason's valley, there is no guitar with him but he has one when he gets to Mason's house.
When Middleton is caught by the posse he has no gun in his holster, despite having two (his own and Ann Mason's) just before he gets on his horse to flee.
When Middleton foils the attempt on the wagons, he wears a white hat. That night at the bar, he is wearing a black hat.
Middleton is captured by the outlaws and is disarmed with his gun being put into a drawer. When he escapes and rides to the rescue he is armed again. Similarly Hank Mason has neither gun-belt nor gun while he is being held captive, but has acquired both by the time he reaches the cattle herd.
The two handwritten letters are from different people (Hank Mason and Tex, an outlaw) but the handwriting is exactly the same in each.
Middleton is riding cross country, he has no canteen, saddlebags or bed roll.