Before Mel sits in the chair to watch the writers act out the money switching sketch, he has full round eyeglasses, but when the audience sees him sitting in the chair, he has half round glasses. When he gets up, they're round again.
When Buddy, Sally, and Rob are acting out the money-switching sketch for Mel, they all have fake names other than their own: Rob is 'George' and Sally is 'Gwendolyn', but Rob calls Buddy 'Bruce' and Sally calls him 'Charlie'.