Character mistake: Barney complains about Andy escorting the Apricot Queen around Mayberry many years prior. Barney had hoped to be her escort. He remembers the date, telling Andy it was "June 23, 1952, a Saturday afternoon." June 23, 1952, was a Monday.
A Black Day for Mayberry - S4-E7
Character mistake: When Opie comes in at the beginning of the episode and asks where Andy is, the exchange ends with Barney asking "Something you want to see him about?" and Opie replying "No, I'll wait," which makes no sense in context. It would have made more sense if Barney had asked "Do you want to leave him a message?"
My Fair Ernest T. Bass - S4-E17
Character mistake: During the party at Mrs. Wiley's, Ernest Bass' girlfriend is called "Ramona." At the end of the show, Ernest T keeps calling her "Romina".
Answer: It was a joke. They were supposed to be dumb hillbillies.
Both. According to later interviews with both Andy and the Dillards band (the real name of the band that played the parts of the Darling children, of which Charlene (Maggie Peterson - Mancuso was also a member) the reason the Darling boys never had any lines was because they would've had to have been paid if they spoke. In return for appearing without lines or pay, Andy promised to get as much of their music onto the show as possible which, he did. This obviously gave them a lot of exposure.