Corrected entry: When the Rojos steals the gold from the Mexican soldiers, one of them uses an automatic machine gun to scythe them down. While it has been poorly disguised as a gattling gun, it is clearly a 'true' automatic machine gun, probably either a Vickers or a Browning. Such guns did not exist at the time the movie was set, not long after the Civil War (The Good, The Bad, And The Ugly, set during that war, was actually a prequel).
Corrected entry: At the Antonio/Marasol prisoner exchange, Ramone says, "Go. Go to him, Marasol." He should have said, "Go to him, Antonio," since he was talking to Antonio at the time.
Corrected entry: After Eastwood has shot the four Baxter men near the start of the film, he turns and walks away. No cowboy is going to turn his back on anyone with a gun - especially after he has just killed four of their mates.
Corrected entry: The first time in the film where we meet Silvanito, he tells Joe that the coffin maker Piripero is so good at what he does "he can size a man up with a glance" to make the impending coffin for him. The last scene in the film where Joe has killed the last of the Rojos gang, Piripero has a tape measure and is scurrying about taking their measurements.