Cory's Alternative Friends - S1-E4
Continuity mistake: Shawn claims his "sister, Stacey" uses the straightening stuff all the time. This is the only mention of her ever during the entire run of the show; and when Jack joins the show he is established as Shawn's only sibling.
Cory's Alternative Friends - S1-E4
Revealing mistake: While Cory and Topanga are handcuffed together, trying to convince their classmates to sign a petition to keep Mrs. Rosemeade, Cory is seen mouthing the lines the others are saying while waiting to say his own.
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.