Other mistake: The pot belly stove in the Sheriff's office has the stovepipe exiting through the front wall, there is no stovepipe or chimney showing on the front of the building?
Other mistake: A female rancher hires workers to dig a water ditch on her property and hires two gunmen for protection. The other ranchers, upset about losing their water supply, vote on whether to fight the woman or let her be. Each man votes by dropping a small stone into a barrel. A black stone means "fight" and a white stone means "let her be." When the barrel is emptied, there are 23 black stones. However, there are only 14 ranchers in the room.
Other mistake: Jeb throws a big party at Miss Kitty's saloon and pays for it with a poke full of gold. Sam the bartender weighs the gold and says it is worth $420. Kitty later gives the poke of gold back to Jeb and tells him, "The party is on me." Sholo, Jeb's mining partner, says, "There's $700 worth of gold there. "
Major Glory - S13-E8
Other mistake: Matt rides into the Cavalry encampment looking for Festus, unchallenged by any sentry, unlike when Festus rode in.
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.
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.
A Quiet Day in Dodge - S18-E19
Other mistake: Festus returns from catfish fishing carrying a gunny sack full of fish that is bone dry when it should be dripping wet or at the minimum damp from the fish.