Other mistake: Near the end of the episode, there's a gunfight, and they show Matt Dillon reloading his gun. Just after the gunfight, you can see the extra bullets on his gun belt. None of the bullets are missing.
Character mistake: When Festus is arresting his cousin portrayed by Shug Wooley, as he helps him up off the floor, he distinctly calls him Henry when that cousin's name is Emory.
Suggested correction: He calls him "Emery." He even says his name earlier in the scene shortly after he walks in and he pronounces it the same way. There wasn't even a character or actor in the episode named Henry, so it's not as if he mixed up the name.
Factual error: In the opening dialogue by Matt Dillon on Boot Hill, the last shot of a tombstone has the date of 1982.
Suggested correction: It's not a "9" but an "8." The two 8's don't really match, but you can see the other tombstone with a similar "8." It's 1882.
Major Glory - S13-E8
Other mistake: Matt rides into the Cavalry encampment looking for Festus, unchallenged by any sentry, unlike when Festus rode in.