Depends what's "the best stuff"... true, it's sad that the "Original Ellington" album was found only after the Mosaic was completed, but still, I consider the Ellington album and the live session (on disc 1 and/or 2) of the original quintet among the best of the box... Lonehill only has the original quintet's two studio albums out, as far as I know.
Oh, I thought the live stuff was on the Lonehill set as well. In that case my original argument is further undermined.
Guy