We'll Have A Good Time Then - S6-E13
Continuity mistake: The picture Rachel takes of Shawn, Jack and Chet is not consistent with the framed picture Jack receives. When Rachel takes the picture, Shawn's necklace is sticking out of his shirt collar slightly and positioned to the right and he has a lock of hair draped over his forehead on the left side of his face. In the framed picture, his necklace is protruding from his collar more prominently and positioned to the left, he has no lock of hair over his forehead, and his left hand can suddenly be seen on Chet's left shoulder. Additionally, the framed picture shows Chet with his head slightly tilted back and showing his teeth as he smiles, but when the picture was taken, his head was level and he only had a slight grin with no teeth showing. (00:04:49 - 00:21:10)
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.