I have the first four volumes of Piers Anthony's Bio of a Space Tyrant in paperback from 1985, and volume five as a softcover from 2011.
The 1985 versions do not have any "author's notes", as most Piers Anthony books do. The 2011 does have one (dated July 1999) - unfortunately it reads like it's continuing a story begun in another author's note (although I'm not certain about that).
Do any of the original editions of these books have the signature "Author's Note"? (If so, please specify which, so that I can try and find them in a physical bookstore or library).
Also, do all of the republished versions from the last decade have a note, or is it only the concluding volume? If the earlier ones do, then a brief synopsis (just a sentence or two for each) would be fantastic - or at least a recommendation as to whether it's worth seeking those out.