Other mistake: The objective of the band is a cache of gold hidden some years ago in the firebox of a wrecked locomotive in the wilds of Northern Mexico. When they finally dig the firebox door out and open it, the strongbox is sitting inside a completely clean firebox, with nary a cinder, ash, or chunk of burned wood in sight. If the loco and cars had been abandoned after the derailment, there would still have been residue in the firebox.
Other mistake: Richard Benjamin kicks in the door to the hotel room to shoot Yul Brynner, a.k.a. the gunslinger. When the gunslinger falls backwards out of the window his black hat never falls off, it stays on the whole time.