I think any current systems copyright legislation is quite irrelevant within underground. As mentioned before, good manners or lets say good intent in general is route to go.
Think for example numerous punk bootlegs, what used to happen in a way that person who did it, was to cultivate the art form. It was often done reissuing rare & impossible to get material, presented in best possible way. Including good sounding material, scans of the original artworks. Possibly extra visuals. Sold for moderate price. Of course most of these happened in times when everything was not readily available from streams.
Nevertheless, when someone does a reissues - whether legit & authorized, or thing called "fanclub release" (hah...), it is not the same thing as bootleg that has sole reason of generating income for abuser on expense of abused. I am 100% sure that still today, it would be possible to see overlooked old rare items and conclude that genre as a whole would benefit of its reissue.
Especially when talking of dead artists: If person making something available is pure with his intent, I feel it is pretty much ok. When you do it out of appreciation and worship, and do not abuse neither artist nor the "scene", I don't think there is need to pull in some bourgeois concepts as "copyright". If nobody is really making relevant income (which should be expectation in case of "noise"), one could conclude this is done out of passion rather than hunger for profit.
When talking of living artists, I do have slight cautions. I do think one should respect the wishes of living artists. For whatever reason, they may not want all their past works made available again. Yet, one can also conclude some people may have lost the perspective. And opposed to their attempts to hide supposedly embarrassing early works, vast genre of art form could benefit of someone just bootlegging the inspiring works would be barely "crime", hah...
For example, if someone out there would make a bootleg box set of S*Core tapes, done with respect and passion... Good quality and moderately priced, I'd buy it instantly!