Other mistake: Al's and Peggy's birthdates are around 1948/1950, respectively. Supposedly, Al married Peggy after she got pregnant the day of his 4 touchdowns in high school in 1966. How could Kelly have been born in 1971?
Other mistake: When Steve wants his money back, Al asks how much was Steve bragging about earlier ($5) he could take and make a fortune, instead of giving Steve $5 it's a $20 bill.
Continuity mistake: The stolen Dodge is a 1974 model. Peggy tells Kelly that she was conceived in it. However, the episode "Christmas" (Season 7, Episode 12) has a flashback to Christmas 1974, showing both Kelly and Bud. Kelly's height had been marked on a door since 1972.
Continuity mistake: Marcy says her parents never let her have a Barbie as a child. In Season 2 episode 14, Guys and Dolls, Al and Steve steal Marcy's Barbie from the basement to sell to buy a new baseball card.
Revealing mistake: Peg is making Al a steak. Problem is the burner isn't even on.
Continuity mistake: The out of order sign on the toilet changes position between shots. It's level at first. Camera cuts to other men. When it cuts back to Al it is tilted. (00:18:18)
How Bleen was My Kelly - S10-E5
Continuity mistake: The family assumes Fox Viewing positions suggesting they are using an antenna to get reception. A few episodes earlier, Al changed their cable television channels to all men channels. You don't need antennae if you have cable.
Suggested correction: Cable and antenna isn't an either/or situation. You can have cable but still use an antenna to get a local channel if your cable provider doesn't offer that station.
Revealing mistake: Kelly is standing by the clock on the stairs. You can see Al and Peg's shadow on the wall waiting for Kelly to come up the steps, so they can come down. (00:02:59)
Plot hole: Al comes home from work. He purposely doesn't look in the kitchen, so he can act like he's surprised it isn't Peg that brings him a beer. Steve talks and Al acts surprised that he's there. When you walk in the front door you automatically see the kitchen.
Suggested correction: It's quite possible to do this. My house has a similar layout: front door opens into the living room, and the kitchen is at the back of the living room. I can come inside and walk to the couch without paying attention to the kitchen. Plus, Al is cranky after work - he says "Ah, what a day" - and he is focused on getting to the couch and relaxing.
This is the only episode where Al does this... Just because he knows it's Steve and not Peg. Pretty obvious.
Just because something is only shown in one episode, that doesn't mean it has never happened before. And because he said "What a day", it seems that his work day was especially frustrating, busy, etc. It's reasonable that he could focus on getting to the couch, not bothering to look at the kitchen.
Factual error: Peg says she did the taxes and claimed 23 children. First of all, you can't. Max number of dependents is 2-3, and second you have to have birthdates and social security numbers for everyone. You can't just write whatever you want and send it to the IRS. And it's a joint return yet Peg says she didn't sign her name. You have to. So in reality, she would get in trouble too since she actually lied on the tax return.
Continuity mistake: Al and Bud are being hunted because they are the final male Bundys. However, earlier, in Baby Makes Money (Season 4?) Al and Peg went to the funeral Of Al's uncle, Stymie. There were other male Bundys. The heirs had to produce a male heir and name him after Uncle Stymie to get all the inheritance. The 3 England Show episodes all have the premise that Al and Bud are the only male Bundys left.
Revealing mistake: When Al slams Kelly's date's head on the banister it moves back and forth indicating it's made of rubber.
Other mistake: When the fat woman gives them the straws, there is no reason why one would already be cut short. They didn't cut the straw. How did they get a short straw?
Plot hole: Al can't eat because his mouth is numb. So they go ahead and eat. Al can eat after the novocaine wears off and Peg can put leftovers in the fridge. They all act like Al can't eat for days and there won't be any food left.
Dead Men Don't Do Aerobics - S4-E2
Other mistake: Jim Jupiter stays with Peg for a week. 6 days later he's shown heavier than he was before. You don't gain that much weight in 6 days.
Just Married ... With Children - S2-E20
Other mistake: Al gets sat on by 3 heavy women. The scale says 927 pounds. 4 more women sit down and the scale says 1071. So 4 more heavy women only added 144 pounds? Impossible.
Flight of the Bumblebee - S10-E7
Continuity mistake: Jefferson mentions having Thanksgiving dinner at Marcy's father's house. Yet, in the pilot, it's mentioned he's dead, as well as her two stepfathers.
Revealing mistake: When Kelly goes for her commercial, you can see that there is a stocking head cover to make her appear bald.
Visible crew/equipment: When Buck is sitting on the couch before Al and Bud come back, the shadow of the camera boom can be seen moving on the stairs.
Continuity mistake: In this episode Al is building a dog house for Lucky. In Season 9 episode User Friendly, we are shown that there already is a dog house, which has electricity and a light.