I had several exchanges recently on the jazz west coast list and the jazz research list regarding sessions recorded for the Keynote label in the mid 1950s that were lost, unissued, but made public in a sense in that they were announced in Down Beat magazine as forthcoming recordings. But in fact the recordings were never released and remain "lost" to the jazz community.
There should be a very few recordings which were published in the sense of being pressed and registered for copyright but never issued - never made available for distribution. Typically, that would occur when the publisher went out of business before release and no one picked up that asset for release.
Mike mrichter@xxxxxxx http://www.mrichter.com/