Crew or equipment visible
Errors in geography
Incorrectly regarded as goofs
Tuco at this time was most likely using Cpl Wallace's gun, taken after he escaped from the train. Blondie would not have recognized the sound of the Corpral's gun.
That battle occurred in early March of 1862 in a mountainous region of New Mexico. The temperatures in the daytime would barely be the mid 50s, with nighttime temps plunging into the 20s or lower. None of the characters are dressed for the what the weather would have been at that time of the year or that location.
First scene is where Blondie comes up on the three bounty hunters who have just captured Tuco. One of the bounty hunters is standing behind Tuco and facing the camera. He should have seen Blondie.
Second scene is in Sad Hill where Angel Eyes walks up on Blondie and Tuco. Tuco, who is digging for the gold, is looking up at Blondie when Angel Eyes comes into the scene.