Plot hole: When Elaine meets Glenn's welfare case worker at The Apartment, the case worker does not tell Elaine that Glenn actually has a wife (after clarifying that she isn't The Wife). This is pure plot convenience. When Glenn's wife finds Elaine in The Apartment, he says "You're home early." She lives there, they are not separated, and surely the case worker would be involved with both of them, not just Glenn.
The Strike - S9-E10
Visible crew/equipment: When Jerry is chasing after Gwen and when he returns to the table, you can see the shadow of the boom mic on the wall. It is most noticeable to the right of the framed picture. (00:20:57)
Continuity mistake: At the beginning of the episode, the bag on the counter keeps moving and disappearing, and reappearing.
Continuity mistake: Donna's purse strap changes position on The Couch throughout the scene, when she's there when George brings up her liking the commercial.
Character mistake: George makes a big deal about wanting to say "I love you" to the girl he's dating and says he's never said it to a girl, just a dog once, and he wants to say it just once. But in s02e01, "The Ex-Girlfriend", George tells Jerry he had to say "I love you" to Marlene when she told him she loves him.
The Suicide - S3-E15
Continuity mistake: When George and Elaine are at the psychic, Elaine is saying she doesn't know how the psychic can put a cigarette in her mouth. At this point the psychic has the cigarette in her mouth and her hands are clasped. In the next shot, the cigarette is now in her hand.
Continuity mistake: When George goes into the suit shop after being told about the sale, he sees another man trying on the suit. George tells the man the sale is on Monday and the man takes off the suit coat and George is holding it in his hands when the saleswoman says the sale is on Friday. In the next shot, she has the coat and is hanging it despite never taking it from George.
The Implant - S4-E19
Continuity mistake: After George puts a couple of the snacks in his mouth, he takes a bite of the next one before Father Jessup says George is great comfort. In the next shot, the snack George is whole and no longer has a bite taken out of it.
Continuity mistake: When Jerry opens the magazine to the article about him before handing it to George, the left side is mostly black with a picture and the right side is half black with "now" in big yellow letters. In the next shot of him handing the magazine to George, the page seen is mostly white with fine print and a small picture. In the next shots of George reading it, the magazine is back to where Jerry had opened it up to the first time.
The Glasses - S5-E3
Continuity mistake: When George bites into the onion, you can see the top of the onion is facing up or towards the camera, next to his finger. In the next shot, you can tell the onion has rotated position. You can see the root is to the side, so the top would be on the side instead of up.
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)
The Calzone - S7-E20
Other mistake: When Kramer is at the restaurant, as a favor for George, he tells the employee that he wants "three calzones." Then the employee just starts cooking the calzones. He never asks what ingredients/filling Kramer wants in those, and Kramer never says.
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.