The late A. Langley Searles’ last Fantasy Commentator is available through Lulu.com for $9.60:
This final issue features an “autobiography” by John W. Campbell, Jr., based on twenty years of his correspondence, as edited and annotated by Sam Moskowitz. This is the final contribution of Sam Moskowitz to the history of science fiction, and was prepared as an enduring memorial to his work and his long friendship to A. Langley Searles.
The appearance of this 164-page paperback surprises me, as I thought all rights to publish the Campbell letters and offer them for sale were held by the Chapdelaines.
The copyright notice in the second volume. The John W. Campbell Letters with Isaac Asimov and A. E. van Vogt, Vol. II [PDF file] reads:
The letter works of John W. Campbell, including the complete Conde’ Nast file of letters by John W. Campbell and also the personal estate file obtained from Mrs. John W. Campbell, Jr., were previously published on microfilm form © 1987 titled The Complete Collection of The John W. Campbell Letters Compiled by Perry A. Chapdelaine, Sr.
Thus, it’s always been my understanding that the Chapedelaines had secured rights to all the Campbell correspondence in the publisher’s office files and from JWC’s personal estate. While an arrangement may have been made, the copyright listed by Lulu.com makes no reference to any earlier copyright.