Norm claims to have occupied the corner stool since the Ford administration. In an earlier episode, a customer who hadn't been to Cheers in twenty years recognized Norm immediately. Therefore, Norm has been a Cheers customer since the Nixon administration (or earlier) and changed stools during the Ford administration.
During the cold opening, Frasier references a safe driving PSA dating from the 1960's ("Guess who Pete and Gladys ran into the other day? Hank and Marilyn.")
Also titled, I Hate Leases to Pieces.