Well, I have listened through the box already and it is pretty incredible. I was surprised at how little of this music I had previously. It turns out that the vast majority of my previous JATP recordings from this period were unofficial and therefore not even included on this set.
I think that Mosaic is under-selling this set a bit in its advertisements. Most of this music is rare. Nothing much of it was ever released on CD with the exception of the Krupa/Rich Drum Battle and the Opera House recordings of Hawkins/Eldridge, Getz/J.J. Johnson and Ella Fitzgerald (A track was actually omitted from the Hawkins/Eldridge CD for space reasons that is restored here).
Hell, there is some Pres and Bean here that is previously unreleased in any form!
I seem to recall that Larry Kart posted here that he was at the September 1957 concert at the Chicago Opera House that included Lester Young, Sonny Stitt, and Illinois Jacquet. Interestingly, it would appear that the LP that was released as the "The JATP All-Stars At The Opera House" included music not from that concert but from a performance done one month later at the Shine in LA. This set presents the known music from both concerts, including previously unreleased performances from Chicago.
I am VERY SATISFIED with this set. Bravo, Mosaic!