Nice piece on the Chicago Reader by Howard Mandel.
https://www.chicagoreader.com/chicago/bob-koester-obituary-jazz-record-mart-delmark/Content?oid=88843266
Not sure everything is in print but a bunch are.
Initially Bob purchased the masters Bill Smith owned and subsequently bought the balance of the catalog.
New York Times - https://www.nytimes.com/2021/05/15/arts/music/bob-koester-dead.html?fbclid=IwAR20k4Zv1ny65sU9j9a-0PGn8Rec0Ep7XF-DYPnwO26m-ySoZHIKHq208lo
I was in Chicago last week and stopped at the store and visited with Bob Junior. He said Bob had a "stroke" in December and was "in and out".
Bob offered me a job in the mid '60s and turned me loose. I will be forever grateful.