In the first episode Jerry calls Kramer "Kessler". The character's name was subsequently changed to Kramer. In the episode "The Betrayal", towards the very end when we see the scene from "Eleven Years Earlier", Jerry is moving into his apartment, and Kramer comes over to welcome him. Jerry says, "You must be Kessler, I saw your name on the buzzer," to which Kramer replies, "No, it's Kramer."
The backwards episode "The Betrayal" is based on a Harold Pinter play, "Betrayal", which also uses the same gimmick. Sue-Ellen Mishkie's fiancée in the episode is named Pinter in tribute to the playwright.