Mosaic Boxed Sets:
9 CD set of Mingus!!! I imagine 6000 alternate takes, plus all the music I already have, plus tons of perfunctory stuff that Mingus never meant to see the light of day.
I am sure there are a few gems I don't have, but I have most of what the unwashed has declared to be essential. The unwashed: that would be us aficionados.
The same reason I don't have the 7 CD Sonny Rollins set, which I really wanted, or the Coltrane Heavyweight Champion set. I already had the individual CDs.
Cheers