It will be fun seeing versions of all that new old stuff turning up in newly legitimate "showcase" covers.
I have posted versions of a number of Charles Ives compositions, and have to admit I did not look too deeply into the rights issue. My understanding at this point is that Ives is already PD in the United States
but a slew of publishers still hold worldwide rights until 2024. In any case, I like this a lot:
“Charles Ives refused to copyright his music, insisting that anyone be able to use it, and scared off publishers by demanding that they make free copies available upon request. However, some publishers after Ives died claimed the copyright on his music! … At first, he self-published and distributed volumes of his music free of charge. In the postscript of 114 Songs, he refers to the possessor as the ‘gentle borrower.’ Sometime following these offerings, Ives granted permission for the publication of his music in the periodical New Music with the condition that he pay all the costs.”
https://logosfoundation.org/copyleft/public_domain_composers.html