Going on from Bob’s apron theory, some guys used to pin the apron they wore to the desk, that way and parts that fell off of the bench would land in the fold of the apron.
I dont know how deep those dowel holes are but I am not sure even if they were quite deep they would be enough to supprt arm rests? It certainly is a bit of a mystery but mystery aside, what a beautiful desk and I am quite jealous 
Paul.
