Legality works both ways, and can be made to defend use of material as well as protect it.                                             
As I pointed out anything pre-1970 odd..(over 50 years) if taped and never heard before, the performer has no legal say. As long as it's previously unpublished in any form, then under the most recent revision of the copyright act in the UK, it's fair game. Though the songs they perform are still copyright works and as you know european article 13 has been passed   Previously published recordings or radio tapes are a different matter and usually hold longer copyright for the performer (Unless pre-1963). But that's all pretty much commercial usage.