Character mistake: When George and Elaine go to the coffee shop after The Movie without Jerry, they establish that Elaine moved to NYC in 1986. Then they make fun of the way that Jerry throws up; both imitating Jerry. The "Dinner Party" episode is after the "The Dog". In the "Dinner Party" episode, Jerry brags that he hasn't thrown up since June 29th, 1980. The black and white cookie ended this streak. Elaine would not have been around to see this, not arriving in NYC until 1986.
The Suicide - S3-E15
Revealing mistake: In this episode when Jerry leaves his room to talk to his neighbour about their fight, when he shuts his door the wall shakes revealing that the place he lives in is not a real apartment.
The Library - S3-E5
Continuity mistake: When Bookman is lecturing Jerry in his apartment, he picks up a navy book with gold lettering and places it on the bookshelf in front of a pink book. For the rest of the shots, the navy book disappears and the pink book is back in front.
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: When George is lying on the floor in his underwear, a newspaper is on his right side. When they take the reverse shot (Jerry's view of him lying there), the newspaper is on George's left side.
Continuity mistake: When Morty is giving Jerry directions to the scuba diving site, The Pen alternates between being in Morty's hand and on the table between shots.
Visible crew/equipment: After Jerry, Elaine, George and Kramer walk out of the orange stairwell, there is a shot as they come out the door. A car drives past. The crew is reflected in the window.
Continuity mistake: In the opening scene in the locker room, George's shoe goes from off his foot to on to off to on.
The Red Dot - S3-E12
Continuity mistake: After Elaine unwraps her cashmere sweater, Kramer wraps the ribbon around his neck in a scarf-like way and then lies back on The Couch. In a long shot of The Apartment (as Elaine exits the bathroom), the ribbon is gone, but when it cuts to Kramer and he asks about The Red Dot (and for the rest of the scene), the ribbon is back.
Continuity mistake: Shot shows a DC-10. Next shot is the inside of a plane that is not a DC-10. Only one aisle. DC-10s have two aisles. (00:00:35)
Continuity mistake: Jerry is waiting for George to come into his apartment and he says to Elaine and Kramer, "my oldest friend is dating the governor", and then folds his arms. In the next shot, as George comes in, Jerry is suddenly holding a glass of juice - there was no time for this change to happen naturally.
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.
Continuity mistake: At The Airport, while deciding to take The Limo, Jerry's scarf moves on and off his shoulder between shots.
The Library - S3-E5
Character mistake: When Marion mentions Mr Bookman she says he'd been on the job for 25 years. Yet later on he tells Jerry he's been on the job since 1971, which in 1991 makes it 20 years.
The Letter - S3-E21
Character mistake: When Lippman is recounting his conversation with his accountant, he mentions that the accountant, a man, gave the tickets to "her daughter."
Factual error: Newman says that the "Magic Loogie" incident happened on June 14, 1987, when the New York Mets lost to the Philadelphia Phillies due to an error by Mets first baseman Keith Hernandez. However, the Mets played the Pittsburgh Pirates on that date, and the Mets won 7-3.
Continuity mistake: While Kramer is explaining about being in the Woody Allen movie, George is in the background looking out the window trying to stop car alarms with his keys. Less then five seconds later, George ends up by Jerry's counter (without being seen) and has a can of Shasta in his hand. (00:08:40)
The Fix-Up - S3-E16
Character mistake: George calls Jerry to tell him about sex with Cynthia. He starts by saying he just got home, which Jerry repeats. A few lines later, George confirms they had sex at his own apartment. Why would he be getting home from his own apartment? (00:13:50)
Answer: The name is Delores. He shouts that name at the end of the episode. Then in a later episode, "The Foundation", he runs into her. And he repeatedly calls her Delores.