I have bought 3 or 4 boxsets of this kind, Django Reinhart, Edith Piaf, and I think Miles as well, but I am too tired to look through my CDs right now. !0 CDs for 9.99 Euros, but that was 5-10 years ago. (yes, 5 years seem such a long time looking back, but they have passed like a blink.) Anyway, I think it had something to do with the difference in the copyrights legislation, between Europe and America (50 years and 70 respectively). Unfortunately, and with no obvious reason other than protecting the big companies, they have passed laws all over the world that increased the copyrights time to 90-100 years, with some exceptions (the Sonny Bono law-it is a travesty of a law...) Anyway this means that all music prior to 1923 is free and new music will not be available free of copyrights untill2024. Of course it is still a matter of the record companies to force new laws that further increase the copyright years. It is a shame, because the original thought from the lawmaker was to help the contributors (composers, artists, producers, etc) gain some money from their work, up to 50-70 years from the original release date, thus ensuring an income for the rest of the life of the contributors and their children (that have somehow been deprived of their parents when creating the music). The 90-100 years newer law, under the new ways of selling and distributing music, clearly helps mostly the record companies. So it is another 20 years for the recordings of Robert Johnson(yes we all have them, but still...)
Back to the original topic, I think that there were many boxsets, mostly Jazz, circa 40ies, but I had not the money to buy them all.And even if I had, I wouldn't have the time to listen to all of them. But from what I have, they are quite a buy.