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."
Plot hole: The Winslows' younger daughter, Judy, disappeared from the show in 1993 (halfway through the series' run) with no explanation.
Answer: It was just cancelled. Read more here: http://www.kellie.de/end.htm.
Myridon