Steve,
Probably, a typo on your part, but Robert's performance along with Brian Setzer was December, 1984 and not 1985. I'm quite certain that is correct. Since, the Honeydrippers' album was released in 1984, that would make sense.
While we're on the subject of this, Robert performed Elvis' Rockin' At Midnight (formerly Good Rockin' Tonight) and Santa Claus Is Back In Town on the show. Is that the only Christmas Song Robert or anyone else in Led Zeppelin has ever performed from the Led Zeppelin days onward? Think about that for a while. That could be a tough one.