Continuity mistake: In the episode with Bette Midler, she is injured when George tackles her at home plate. When he hits her, she is knocked into somebody. When they show her again, she is sprawled against the backstop with no one behind or even near her that seems to be hurt. George also misses home plate.
The Doodle - S6-E20
Continuity mistake: In this episode, Newman's apartment number is 5F but in all the episodes both before and after, The Apartment number is 5E.
Continuity mistake: Right after Jon Voight enters the taxi, Kramer sticks his arm in through the cab's rear side window, where Jon Voight was sitting. Jon Voight grabs the arm and bites Kramer on the wrist. As Kramer later was describing the incident to Jerry and George, he was pointing to a bite mark near his elbow.
The Gymnast - S6-E6
Continuity mistake: When George is at his girlfriend's mother's house, the plates on the table switch around. Then the order he stacks them changes. When he picks them up, the plate with the chicken is in the middle with a plate with a napkin on top, then in the kitchen, the plate with the chicken is on top.
Continuity mistake: Kramer takes an awkward Polaroid of Jerry for his wall, but the photo on display is an ordinary print. (00:09:45 - 00:12:00)
Continuity mistake: When Elaine gets kicked out of the nail salon it is a clear day (in fact the whole episode is) then the next scene she meets J Peterman at night and in the rain. When she left the salon she is wearing a red blouse, no jacket. When she meets Peterman she is in a trench coat with a white blouse. The Peterman portion of this episode really makes no sense.
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.