In one episode, Blanche says, "Dorothy, I've given this a lot of thought. I've had 4 kids, I've never had a Mercedes. So, which one do you want? Biff, Doug, Skippy?" However, Blanche has two daughters, Rebecca and Janet, who both made appearances on the show. She also states in "To Catch a Neighbor" that she has a son named Matthew, which would give her 6 children, not 4.
As with any long-running show there are many inconsistencies between episodes. Characters' life histories, their birthdays and ages are reported differently from time to time as the writers invent new stuff for them that wasn't thought of when the series began. "Facts" are altered to fit the jokes, and a good deal of leeway is allowed.
Depending on the episode, Dorothy either had no date for the prom and got pregnant by Stan, went to the prom with Stan and then got pregnant, or had another date to the prom who didn't show up and got pregnant by Stan. (Any way you look at it, though, Dorothy got pregnant by Stan.)
In the episode dealing with Rose's drug addiction, she jokingly states that this was the anniversary of her cat "Fluffy"'s death, and Dorothy reminds her that she never owned a cat because she was allergic to them. However, in at least one other episode, Rose spoke of having a cat. In addition, she also stated his name was "Lingstrom" rather than Fluffy.
In regards to the show in which Rose is fighting her addiction to pain pills and how she is allergic to cats, in one show where Blanche is reminiscing about how she first met Rose, Rose had a cat, Mr. Peepers, which she offered to a little boy to keep when Blanche later said that it showed her that Rose had character.
Dorothy and Stan got married because Dorothy got pregnant and they were married for 38 years. In one episode, they mention that Michael was the one conceived first, yet even though his age changes in different episodes, he's always in his twenties when he should really be in his early forties.
In many episodes it is said that Dorothy married Stanley because she was pregnant and that they were married for 38 years at the time of the divorce. The odd thing is that neither of Dorothy's children are even close to being 38 years old.
In the episode where a robber breaks into the girl's house, Rose gets paranoid and buys a gun. When she returns home, she said she learned how to shoot the gun in the "basement of the store". Basements are not allowed in Miami, Florida.
The layout of the house is entirely illogical. Not only does it not match the exterior shown, but the lanai is not in the back of the house, it's on the side of the front. The back hallway of the kitchen does not lead to the garage, it runs into the hallway to the bedrooms. The hallway to the bedrooms exists by itself, as either side of it leads to the kitchen or the backyard. The door on the side of the garage is on the wrong wall according to the layout of the kitchen, and the exterior of the house.
In the first episode that Michael appears, Dorothy says that he is 29, but later when he is to marry Lorraine, he is 23 and she is 44. Then when he comes a third time, he doesn't mention his child at all when she kicks him out of the house.
The background set with two elevator doors is used as the backdrop for numerous interiors: the museum where Blanche works, the counseling center where Rose works, and the city hospital to name three. Also, the museum where Blanche works was used as a psychiatrist's waiting room.