Revealing mistake: In the episode where Steve is helping Richie with a science project, Steve turns on the tornado machine which malfunctions and causes a very powerful wind to blow through that begins to decimate the kitchen. While this is happening, Richie is forced through a door and out of the kitchen by the wind. When Richie is again, as he is holding onto the doorway, support wires are attached to him lifting him up.
Revealing mistake: Carl, Eddie, and Steve are out ice fishing. At one point Carl falls through the "ice" and you can clearly see that the "ice" is made of some sort of styrofoam. It looks like the stuff used for packaging. The snow looks just as fake.
Continuity mistake: From the outside of the house, you can see the staircase and door are to the far left of the house. But from inside the house, you have a fireplace and the staircase to the right of the door. So you know it's not the same house they use in the show.
Other mistake: In this episode, they have a leak in the roof. Yet, the house is a two story house with an attic. So it should not be able to leak into the living room. Also, when Carl and Eddie go up to fix the roof, Eddie falls through the roof and ends up on the living room couch. Again, two story house with attic. Should not happen.
Plot hole: The Winslows' younger daughter, Judy, disappeared from the show in 1993 (halfway through the series' run) with no explanation.
Visible crew/equipment: In the episode where Carl is "fishy sitting" for his boss, Steve is explaining to the boss how he swallowed the fish. You can clearly see the studio lights reflected in Steve's glasses.
Continuity mistake: During the scenes where they play Mortal Grandma (or whatever it's called), the characters' health bars don't change.
Continuity mistake: Carl says that Laura was five years old when the movie "The Wiz" was released, which was in 1978. That would mean Laura was born in 1973 and is or will be 24 years old. She only finished high school in the previous season.
Dream Date - S7-E22
Continuity mistake: Laura says that Steve asked her to be his prom date when they were six years old. In other episodes, she has mentioned that she first met him as a blind date - their date in the first season.
Rock Enroll - S5-E13
Visible crew/equipment: Towards the end of the show when they bring the cake out for Steve a crewmember walks past on the right of the screen.
Other mistake: Even though this is the first time that the kids are being introduced to the "Urkel Dance," Maxine is mouthing the words to the song as she dances.
Continuity mistake: Whenever the characters in this sitcom fall through the roof, they end up on the living room floor. The house is a very conventional design with a second floor and an attic, so they should end up in the attic or on the second floor.
Who's Afraid of the Big Black Book? - S9-E5
Continuity mistake: Eddie's birthday appears to take place during the spring or summer. But the episode "Son" showed that he was born in January.
Visible crew/equipment: When Eddie drives his car through the front door, when they show the hole he made with the car, look at the very top of the screen, the sky stops and you can see a good two-three feet of sound stage.
We're Going to Disney World (1) - S6-E22
Continuity mistake: In an earlier episode, Steve told Carl that he has to take charter flights because he was banned from all commercial airlines. Yet, in this episode, he takes a commercial airline to Florida.
Dream Date - S7-E22
Other mistake: Steve and Laura kiss at the prom, and the moment is never mentioned again. In fact, during the Season Nine episode "Drinking and Jiving", Steve is surprised when Laura kisses him passionately, while she is drunk. He is surprised enough to mention it the following morning and offer to start a relationship (then Laura pretends that she doesn't remember).
Continuity mistake: Carl tells the establishment's owner that Eddie and Waldo are under the age of twenty-one. However, in the episode "Best Years of Our Lives" (also Season 7), Waldo tells Maxine that he worked on a parade float every year in high school, which makes seven floats. If he failed three grades and started college in the previous season (with Eddie), he would be at least twenty-one years old by now - probably twenty-two.
My Broken-Hearted Valentine - S3-E18
Other mistake: When Steve is wearing his Cupid costume and waiting for Laura in the Winslows' living room, the doorbell rings. He is obviously excited and ready to pose before seeing Daniel there. This does not make sense because Laura would not ring the doorbell to enter her own home. In fact, she does not ring it when she does arrive shortly after Daniel.
Rock Enroll - S5-E13
Visible crew/equipment: When they are singing happy birthday to Steve near the end of the episode, a crew member can be spotted in the top right corner walking past an open door. (00:20:55)
Plot hole: The history on Urkel's Isetta is all wrong; in one episode he mentions that he paid $4 for a sunroof that he claims he bought used, however his uncle paid him $50 to take it away. In another, he claims his car has a speedometer that goes up to 30, but before it had a chalkboard. In "Hot Rods to Heck," the speedometer goes to 60 mph. The car would also screech, putter, sputter, smoke, break down, etc. but it seemed to be just fine in "Driving Carl Crazy," ''It's Beginning to Look a Lot like Urkel," and "Hot Rods to Heck."
Answer: It is said that as Steve Urkel became a more popular character on the show, Judy became less important to the storylines, plus either her or her parents were demanding more money, causing her to be removed from the show entirely.