If Music Could Talk

I was playing some stuff by Edwyn Collins recently and realised I'd lost a Black Sessions recording of him on a disc crash years ago. (If anyone has a copy please PM me) It started me thinking about the dearth of such material by The Clash and off shoots. How many quality recorded radio sessions were ever made or saved by Joe Strummer or Mick Jones? I know The Clash never finished a John Peel Session, but when more music was being broadcast all over the frequencies, where were they?