Thanks for the great discussion! Looking at the straight on shot above, you can see the 15th fret ivoroid projects out from the fretboard less on the bass side than the treble side. I got out my new Siminoff drawings, and he shows the neck offset this way, with the bass side ivoroid at about 5mm and the treble ivoroid about 8mm+. I understand what Jamie is saying about the centerline of the top joint being off, but if you use the apex of the heelblock as the upper midline, the neck is definitely offset to the bass side, regardless of where the top joint is. Interesting. I planned on retooling a bit on my next mandolin, so I will incorporate this detail!
"No point in thinking outside the box until you know what's IN the box. . ." #Frank Ford