On the show, Jerry lives on West 81st Street. However, when in Jerry's apartment Kramer tells Elaine and Jerry where they can find a man's fur coat, he says, "Just go down to 88th Street." Should have been "up" to 88th Street.
Whenever we're shown the inside of Kramer's apartment via the peephole looking in, there's what appears to be a living room immediately in front of the door. However, when Kramer opens the door a wall is in its place, contradicting what the peephole reveals.