Continuity mistake: Towards the end of the episode, it transitions between the Yankee ball at night and "Susie's" wake which is during the day.
Continuity mistake: When Mike accuses Jerry of murder at Susie's wake, watch the people behind and around Jerry. There are women either side of Peggy, turning around, looking surprised and moving their hands. The next shot, we see Jerry from behind his seat, and everyone has instantly changed to sitting perfectly still, looking ahead with their hands still.
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.