New material from Billie Holiday, Coleman Hawkins, Herchel Evans, Lester Young and others surfaced when the son of audio engineer William Savory donated recordings of about 1000 performances to the National Jazz Museum.
The Museum is cleaning and digitizing the recordings.
Only excerpts can be offered because of the way copyright laws work.

Although the Museum paid for the recordings, the music cannot be distributed until the estates of the musicians can be located and compensated. Many are difficult to track down.

Jazz Museum officials are hopeful that a blanket payment to the American Federation of Musicians might solve the problem.
NY Times, Editorials, Sept. 2010.