One of the previous owners contacted me and told me that it had originally been a 6-string bass, but he thought that was redundant since the fretless neck was already in the bass range. So after speaking with Rick Turner (who was involved in building the bass) he decided to have it strung as a baritone, from A to A, between bass and regular guitar. Also, the 6-string neck is 30 scale, like a Bass VI - an instrument that I really like too!
Actually, the term baritone is not strictly defined. I personally consider the Bass VI to be a short scale extended range bass, but I know other people approach it more like a guitar so for them it might be more of a baritone.