Yes, Stewie, a lot of information but no answers for Rick Fielding's friend as to "EARLIEST" copyright. Were either of the unissued Jackson takes copyrighted? Or the Whistler version? And were either of these "Jailhouse Blues" and not "He's In the Jailhouse Now."? Whistler's seems to be of that song if I read the posts a-right.
If you have the books, perhaps you can check them for possible data on copyright.