I do the same! I preorder every set I'm interested in (at least at 60%), and so I did with the Ellingtons, the Basies, Goodman, Shaw, and quite all the recent sets. I wait the "last chanche" opportunity only for boxes I'm not interested in (the Dinah Washington, for example ) only for completeness... This time things went bad.
But I think the way to help Mosaic is to PREORDER sets. I can't wait the promised Ellington '30s, and I still hope in a Victor Goodman big band (you know the awful remasters of "Birth Of Swing" set).
Much the same for me. If I want something I try to get it as soon as possible, pre-ordering usually. This goes back to my collecting days when if you didn't grab something when you saw it you were likely never to see it again. This may just be a UK thing because US/Japanese/Euro imports of lps and cds were often here today gone tomorrow.