A couple of additional thoughts. For me, 14.2pcf seems quite high for hay. That would imply that a 2'x2'x4' bale weighs 227lbs. Every year we load our loft by throwing 500 bales over our heads. I believe a lightweight bale to be 25lbs and a heavy weight bale to be 40lbs. At even 50lbs per bale that's 3.1pcf. The day I run across a 200+lbs bale of hay is the day I stop moving hay!
The few Pennsylvania Dutch barns I have seen appeared to be more heavily framed then the typical New England barn. The vast majority of older New England barns are lightly framed by today's standards. Some of those barns have quite large haymows that could support over 20' of hay and have served as working barns for up to 200 yrs. I would not be comfortable using older barns as a basis for today's design load criteria, but I am comfortable to use them as a conformation.