About the only thing I can add here is that we should never give up hope with regards to anything considered missing.
I was told to give up on my obsessive search for all of those "missing" AVA masters. I never gave up and then one day I had the actual three-channel session masters in my hands... in mint condition no less. I recall all the comments years ago about how The Black Hole could never happen because of the obsolete 1979 digital format. I never gave up and then one day Disney had the masters ready for our "co-branding"... in fabulous condition no less. After years of searching and being told "no complete scoring elements exist" I awoke one day to have Sony and Chace sending me what turned out to be the complete original cues for On The Waterfront. I also recall being ready to end a two-decades long search for any music-only elements for Cromwell only to have them show up in full stereo, mislabeled inside Columbia Pictures boxes containing the dialog and sound effects elements.
A few years ago Varese released an expanded Great Train Robbery but informed listeners that a key action cue was "lost". A few years later we released the same score... this time with that "lost" action cue.
And my 'never-give-up' feelings were really stoked when the "totally lost" masters to Elmer Bernstein's See No Evil suddenly turned up... complete and in stereo no less.
These are just a handful of my own experiences. I'm sure other labels have similar tales.
Hopefully these discoveries instill a little bit of hope in you folks that other "missing" treasures may still be out there. I refuse to throw in the towel regarding Hugo Friedhofer's Joan Of Arc - albeit admittedly I'm not holding my breath.

--Doug