Kevin, though I don't know about the marks, Sam is real big on templates. I would guess that they mark the different stages of a curve on the scooping out of the seat. This chair was a part of an 8 or 12 chair order to go with a huge walnut slab dining table. The normal dining chairs were too small visually so they over-sized everything for this set.
One of the shockers for me was that in the initial cutting they nailed the templates to the wood for the arms / legs / spindles! They either do that before jointing and planing or they fill in the holes with epoxy and sawdust.
I only went there two days ago so I do not imagine that he is feeling better yet. If I hear anything through the show at our local art museum I'll post it.
Veni Vidi Vendi Vente! I came, I saw, I bought a large coffee!