I love your cynicism and unfortunately agree. There are institutions like ASCAP whose job it is to collect revenue from plays and sales of copywritten music. My family still receives royalty cheques from music written by my father in the late 1920s. I don't know if it's possible to even tell them NOT to collect and let the copywright lapse. It's not in their interest as they make a % on anything collected. The tide is certainly turning much more towards enforcing copywright as the internet erodes the prospect for holding on to one's creative efforts in order to make $$. It's not a simple matter, but you can be guranteed that wherever there is $$ to be made and litagants who smell an opportunity, it will get tied up.
A possible solution might be for the curators of the collection to "sell" downloads with funds going into an accont that can be dispersed at some point in the future when all of the copywright holders can be contacted. Would probably require the approval of any/all of the recording companies who had those artists signed to exclusive contracts at that time. Collecting $$ ensures that all those greedy SOBs have the potential of grabbing some $$ whareas to do nothing means that no $$ are being collected.
My family has an enormous collection of scratched old 78s and original recordings (we had a machine that cut records). I have no idea what's in there and frankly don't care. Many of the records and privately made discs were made by my father with his music buddies. Not sure who's on them, but he had in his radio orchestras (that's what they called bands at the time) some up and coming youngsters who later became well known like the Dorsey Brothers and Benny Goodman. He also played with other bands and recorded with Bix Biederbecke, Duke Ellington (Jungle Band), Paul Whiteman, Joe Venuti, Jack Teagarden, etc. Anyone want to throw money at my family? The collection is at my sister's place in Victoria BC.