Revealing mistake: When Cory opens up the curtains of his bungalow to show Topanga the beach, you can tell the background is just a backdrop, as there are no waves approaching the shore. (00:10:36)
Revealing mistake: When the noir version of Eric is talking about the noir version of Jack as he is playing the piano, you can see Jack is just tapping his fingers against the piano keys and not actually striking them. (00:05:33)
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.