I've just started dipping into this and so far it's pretty astonishing. Niven was a high school teacher and record collector who made tapes of what are basically narrated histories of particular jazz musicians. They're sometimes quite detailed - Ellington runs to 90 tapes with an additional 7 for sidemen. (Which may sound odd to non-jazz people but I have some CD collections of only Ellington sidemen and it's great stuff.) This is very much a fan's project, one reason that somebody like Bud Freeman gets more tapes than Charlie Parker - a longer career sure but still.