One year when I was in college, (late 1970's), I was one of the DJs for the campus radio station. It was only broadcast within the student union building cafeteria. I had the last show on late Friday afternoon, usually with a listening audience of between 0 and 5 people. I could play anything i wanted to.
One day near the end of the school year, the station manager said that about 30% of the 45 RPM records had to go, to make room for new incoming stock. All of the DJs were invited to help themselves to anything he had deemed redundant.
I had last pick, so I looked through everything remaining, with my eye on hidden gems, radio station promotional copies and rarities - ultimately I selected about 25, and a couple of years later, I traded most of those to a guy for the then recently-released three album bootleg
Live in the Promised Land, sourced from a radio broadcast of Bruce Springsteen and The E Street Band at Winterland in San Francisco. from December, 1978.
One of the 45's I kept was a promo copy of
Knock on Wood from David Bowie's 1974 album
David Live. The B Side was
Panic in Detroit, from the same Philadelphia shows from which the live album had been culled, but not included on the album itself. Other than as a 45 B side, this song remained unreleased until a 2005 remixed CD reissue. This version features a great guitar solo by Earl Slick.