Well there is one original drawing set, and then 
photocopies are made for the workers who need it.

I have a Yami no Matsuei settei set, and I still 
really dont know if its a studio copy or a copy 
of a copy.  Some of the sides have been "cut 
off" by the copier and since then I've seen 
another YnM set with pictures where the sides 
WEREN'T cut off, mine might be copies-of-copies 
afterall, unless someone at the studio didnt 
know how to work the copier properly :P (but 
then again, their set had less sheets than mine 
did...so who knows)

Theres probably no way to really tell.  It would 
be nicer to have a set that was actually 
physically used by one of the workers, but, I'd 
say the only way to know that for sure would be 
to get the actual original hand-drawings.  (I 
wonder how much THAT would go for!)

I would personally NEVER make copies of my set 
to sell/give to someone else.