How do you write the authorised biography of a person who does not seem to exist?

When I was first approached to write the definitive biography of Davey Dreamnation—an invitation I was, obviously, more than happy to accept—I was given to understand that I would have unfettered access to Dreamnation’s personal archives, including his astonishing collection of unreleased songs; his musings in writing on the parlous state of the music industry; and his unparalleled…