It bears repeating that this was planned for release, so Blue Note was satisfied with the date. Parker's death, and possibly poor sales of the previous release, may have been the factors that cancelled the release.
It's easy for many to assume that unreleased material is not up to snuff, but we have to remember that Blue Note was a small company, and couldn't afford many releases that didn't turn a profit. There are numerous sessions that are of a very high caliber, but which weren't released strictly for commercial reasons.
Parker's music may have not been at sufficient a creative level to satisfy all the critics (he has been dismissed on more than one occasion as an R&B player), but it is good strong blowing, and I love it.