Here's what Mosaic says about the leasing situation:
Why Limited Editions? Mosaic does not own Pacific Jazz, Atlantic, Columbia, RCA, Blue Note, Verve or any other catalog product. With the exception of our Benedetti/Parker set, we lease all of our recordings from other record companies. The leases vary in detail, but in every case there's a cap on either the number of units we are allowed to manufacture or the number of years we're allowed to offer the set for sale. Therefore once the set has sold out, it will not be made available again.