Leo,
I must recommend not to use Treadwell & Wood's book "German Knights of the Air" as it has numerous factual errors! I've bought it myself and have regretted it ever since. The quality is so poor one needs other books to verify the info given. As a good example, compare the bio's of
Rudolf Berthold and
Hans-Joachim Buddecke and see a blatant error or two. The Rumey chapter also has a huge mistake, by stating he was born in Bavaria.
My recommendation is to leave that book in the stores and save up more money so you can buy a good book instead, like
Above the Lines.
As for Jacobs, Neal O'Connor did a few interviews with the good man in the 70's and Volume V of Neal's "Aviation Awards" series has a large chapter on JJ, including many pictures. It's about 40 pages.
Other than that, I only have some scattered info coming from Above the Lines and less notable sources. It is indeed strange to see such a long-lived man being given so little attention. Denver, Colorado (Wings over the Rockies Museum) holds one of Jacobs' uniforms as well as some other items of his while the medals supposedly reside in a private collection (they did in 1990).
Perhaps our own Gary Jacobs has a bead on some other valuable sources?
Kind regards,
Reinout