Continuity mistake: Jerry's apartment in the first episode was on the fourth floor. Then in the next bunch of episodes it was 3A. It then changes to 5A for the remainder of the series.
Continuity mistake: In the pilot episode "Good News, Bad News", look out when the waitress discusses the two coffee pots. She says "Trusts me George, nobody wants to see you on caffeine", and the unbuttoned top of Jerry's jumper is noticeably folded - but straightens instantly in his reaction shot. Also it should be noted that she walks away without actually pouring coffee to George - you have to assume a little amount of time elapsed between that reaction shot with Jerry and the following on George. (00:01:45)
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.