Factual error: In the season 3 opener, Sophia befriends an elderly gentleman and spends much of the episode on a boardwalk in Miami Beach. The set design, however, replicates nothing even close to Miami Beach. Instead of chrome and neon Art Deco it looks like a northern fishing village complete with netting and buoys.
Other mistake: Blanche asks Daisy to go to Rose's room to get the things she set out for the rummage sale. Daisy goes into the first room on the right and gets the items, including Rose's teddy bear. Blanche gives it to her for helping out. Rose comes home, goes to her room and comes back asking where her bear is. Problem is, Rose's room is at the end of the hall on the left.
Revealing mistake: When Dorothy and Blanche are in Rose's room, look at Baby. Its very obvious its just a stuffed toy pig. You can tell by the fluffy skin, the unnatural ear movement, and the covers would be moving up and down as its breathing. You can really tell its fake when Rose gets up off her bed.
Continuity mistake: In this episode Blanche says she has had 4 children, but she has never owned a Mercedes. She offers one of her three sons (named Biff, Doug and Skippy) to Dorothy in order to let her keep the car. In other episodes she mentions daughters Rebecca and Janet frequently, and in the "To Catch a Neighbor" episode she mentions a son, Matthew, who is a CPA. That's at least six children by my count.
Other mistake: It's raining outside. Dorothy comes in the house and says "it's really coming down", then shakes her coat off although it's not wet. Then Stan shows up with an umbrella that's not wet. Then Sophia's brother Angelo shows up and isn't wet either.
Continuity mistake: About three minutes into the show Dorothy, Sophia and Stan are in the living room. Sophia is trying to convince them to pretend they are still married while uncle Angelo is visiting. Dorothy is wearing a large pair of earrings, but at one point during their discussion when they show a close up of her, the left earring is suddenly missing. A second close up shows the earring still missing, but as Dorothy turns her back to the camera, she reaches up and touches the remaining earring. In her next close up, she is wearing both earrings again.
Factual error: Angelo claims he promised their mother on her deathbed that he would become a priest, and Sophia says she promised she would marry someone else - and we assume she died before Sophia or Angelo got married to their spouses. However, in the episode where they are flashing back for Mother's Day, Sophia's mother is in this episode along with Sal (and she looks like an older version of Dorothy).
Revealing mistake: In this episode Dorothy and Blanche are awakened by a stench coming from the kitchen. After they go to inspect, we see that Rose is making some sort of Krispies treat. As you see her carry the plate to offer Dorothy and Blanch one, you can see that the plate is empty. And once they all start to eat them you can easily see that none of them are actually picking anything up and putting in their mouths.
Plot hole: Dorothy's son Michael is twenty-two years old in season three. When Sophia and Dorothy reminisce Brooklyn, NY, 1954, Dorothy asks Sophia to babysit her children, one of whom is Michael. Sophia refuses, so Dorothy says "I'll just leave them with Stan's mother." They talk about Michael screaming when Stan's mother was watching over them. If Michael was a baby in the fifties, he should be in his thirties in season three.