Continuity mistake: Chet says he's spent the last year searching for his wife, but, when he left, Shawn was ending 7th grade and now Shawn is supposed to be sixteen.
Continuity mistake: When Virna is standing in the doorway of the trailer, her left arm is touching the curtains near the door. When the shot changes, her arm is instantly down at her side.
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.