Continuity mistake: When George and Jerry are discussing Elaine's poor dancing, The Keys that are sitting on Jerry's kitchen counter inexplicably disappear between shots. (00:04:10)
Continuity mistake: In the theater, before The Movie starts, Brodie has his right hand on the outside of the candy bag in one shot, and suddenly in the next shot his hand is reached into the interior of the bag. (00:07:20)
Factual error: In the scene where Anna is standing with George beside his father's GTO, Elaine suddenly runs in and pries her away from George. Elaine and Anna get into the cab. As the cab pulls away, the side door is marked as an NYC cab with a taxi license number, etc., but the license plate in the back is a California plate.
Character mistake: When George tells Jerry about his date with Anna, he says he is picking her up in his father's 1968 GTO, but the car he is leaning on in the park is a 1967 GTO, which has a completely different body style.
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.