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.
Factual error: Dragon's dog, a Rottweiler, was not in the US until 1931, much later than the show.
Suggested correction: The Rottweiler is considered one of the oldest breeds. It was only in 1931 that the American Kennel Club recognized the Rottweiler as an official breed. There's a difference between a breed existing and being recognized by a kennel club.
Other mistake: At the beginning when Festus rides up and finds Riley Sharp handcuffed to the hitching rail, if you notice the handcuff chain is draped over the top of the hitching rail and there is nothing preventing him from sliding the chain off the end of the railing.
Major Glory - S13-E8
Other mistake: Matt rides into the Cavalry encampment looking for Festus, unchallenged by any sentry, unlike when Festus rode in.