Continuity mistake: At the beginning of the show, when Jerry is having a massage, his hands are in front of him, under his chin. The position of his fingers change considerably after The Masseuse says, "I don't know" but then return to the original position in the next shot.
Continuity mistake: While Jerry is having his massage, The Masseuse walks around the table to reach his right side and we can then see two items of clothing, one blue and one grey, hanging on the clothes stand behind them. During the rest of the scene, we only ever see the grey item hanging there.
Chosen answer: George does mention his brother in the episode "The Parking Space". They actually really never mention anything that contradicts the fact he had a brother though, it just isn't mentioned.