Hi Tony,
I had assumed most of us here bought Songbook for the 'unreleased' and 'rare' songs that were included. I never even noticed what was not included to be honest. Oh and we bought it to help support our favo(u)rite artist maintain the lifestyle that he's accustomed to, LOL. I don't think Songbook was intended to be a 'every track ever recorded' type thing like Bear Family puts out, IMO.
Bill