Visible crew/equipment: After Mr. Feeny says "You are the graduating class of the year 2000," he turns around in front of the back wall. As he turns around, there is a shadow of possibly a boom mic on the back wall which moves as Mr. Feeny moves. (00:04:15)
Other mistake: Eric is showing Feeny the doll he has and pulls the string to make it talk. When he makes the doll do mission impossible, he pulls the string but the doll doesn't say anything. (00:03:47)
And in Case I Don't See Ya - S6-E10
Continuity mistake: When Cory, Shawn and Feeny are at the table, Feeny's glass is almost half full. Cory later fills it up, but in the next shot the glass is half full again. In a later shot it's full and then it's somewhere in between half full and filled up.
Continuity mistake: In the beginning of the show, Cory is showing Shawn something he wrote in the school paper. Cory walks away leaving his backpack on the bench. In this whole scene to the point where Cory says, "Is it just me or is it just me" sometimes he is wearing his backpack, and sometimes he isn't. (00:00:20 - 00:03:05)
Santa's Little Helper - S1-E10
Audio problem: When Amy is playing the piano with Morgan, the last few notes that they play while the camera is focused on them are out of sync. (00:19:50)
Plot hole: After Shawn leaves Cory's house to get a pizza, he calls Cory on the phone literally a minute later to tell him that Lenny Dykstra is at the pizza place. There's no way Shawn could have left Cory's house, walked to the pizza place, spotted Dykstra and either asked to use the restaurant's phone or found a pay phone to call Cory in such a short amount of time. (00:13:30 - 00:14:45)
Answer: Topanga's middle name is never specified. Considering her sister's name is Nebula Stop-the-war Lawrence, Topanga's is probably something equally unusual.