Yeah...it was a great show...Jackson was touring behind his first album, and he played two sets that night.  I was there for the first set, and we raced home across San Francisco to hit the "record" button before the second show started.  I recently discovered that the first set was recorded but not broadcast...so somewhere out there on a KSAN pre-FM reel is the show that I attended.

As for the Bowie/mono issue:  could it be that the circulating show was sourced from a cassette tape recorded by a fan, rather than a radio station reel, or a soundboard?   Back then, a lot of receivers has a MONO/STEREO toggle switch for FM.  Stereo FM reception was often plagued by FM static, and dodgy reception could be improved by switching over to Mono.  If something can go wrong, it will, so it wouldn't surprise me to find a home taper discovering that he was recording in Mono three songs into the recording....having done it myself. 

I don't know when KSAN switched to stereo broadcasting...but they definitely were broadcasting in stereo by 1974.   Do you know when the BBC began broadcasting in stereo?