acman, not to sound contrarian but for any artist as popular as Coltrane I wonder why a recording would be held back and not issued? Could it have been that Coltrane himself was not satisfied with it? Or someone at Impulse was disappointed? Contract issues?
From what I read it was not lost, 'Trane himself had a copy of the tape. It seems he had enough clout to push for a release if he wanted to.
And yet we hunger for more from favorite musicians after they are gone. So there can be a ready market for "anything" that has a delayed release. Maybe we'll be lucky and it is an unheard masterpiece. I admit I do enjoy the Monk/Coltrane concert recording discovered a couple of years ago, so not all "newly discovered" tapes are second rate.
https://www.youtube.com/watch?v=dgq_QZ74VI0 Listening will tell all. ;^)