I believe quite a lot of early stuff survives in the archive, but a high proportion of the more recent recordings (i.e. of the "current revival" performers) was not preserved. There doesn't seem any consistency; there have been three June Tabor CD releases from "The Peel Sessions" (don't know how much their contents overlap, though), whereas I think Ralphie recently indicated that almost all the Nic Jones recordings have been wiped.

George