Lincoln, Davis and Booth: Family Secrets

[Eva Elisabeth]

Mr. Cowan, several biographies and other works by respectable scholars were published after 1969, like Bill, I never came across any mentioning these "groundbreaking" secrets (after 148 years of intense research or 104 in 1969!). Why do you think is that?
I tried to google the author's reputation, but drew a blank (exept for facebook and twitter...), so I'd second Bill's last post.