Factual error: On the bottom of all checks, they have the routing number, followed by the account number, followed by a repeat of the check number found in the top right corner. When we see Jerry's bounced check, "1246" isn't seen after the account number.
Continuity mistake: While Jerry calls George from the coffee shop to tell him about the survey question, there is a shot of the waitresses and staff sitting at the tables. Behind them you can see the booths the gang usually sits at and there is a wall right next to the booth with pictures and pipes. Only problem is there are always booths next to the two near the front entrance. Even in this episode you can see the other booths as there are menus, condiments and napkins at the booths next to the regular booths.
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.
Revealing mistake: When Kramer and his lawyer, Jackie, are in the taxi; when Jackie says "who told you to have a pow wow", a man is seen walking across the rear window. The taxi is supposed to be moving, but the man's position stays the same (the taxi should be pulling away from him). The actual traffic filmed for the green screen doesn't seem to react to a man jaywalking in front of them either, as it was someone walking across the set.
Continuity mistake: After crazed Jerry and Elaine leave to get a hat, Kramer picks up the tub of ice cream Jerry had set down and starts to put the lid on. In the next shot, he's not holding the ice cream.
Continuity mistake: In one scene George's desk is placed with room to walk all around. When Steinbrenner walks into George's office, the desk is pressed against the wall and office looks smaller. (00:18:54)
Factual error: The grocery store that Kramer walks into with Little Jerry has a round doorknob. Those were phased out of public use in 1992 after the Americans with Disabilities Act took effect, but this episode takes place in 1997. (00:09:45)
Audio problem: When Kramer is telling Jerry about Little Jerry as he exits The Apartment, Kramer finishes his sentence with the word "jealous", and the S is audibly cut off in the middle, as if the audio was spliced there. (00:14:25)
The Fatigues - S8-E6
Continuity mistake: When Frank breaks open an egg in the close-up of the pan, we see there are more than half a dozen eggs in the carton. However, in a wideshot of the kitchen, the carton appears to have only about three eggs. (00:16:15)
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)
Continuity mistake: After George and Jerry discuss the fact that George will never have sex again, they stand up to leave the coffee shop and George places a large book under his arm. In the very next shot, he is holding the book in both his hands.
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.