An interesting sword, are you sure that the unique pommel ring isn't unique to the American-made example?  
 
It might be me, but I don't see it represented in any of the other photos you post. It looks like on those, the guard terminates in the pommel.  
 
Possibly an American variation? I'll see if I can dig up similar examples in my copy of George C Neumanns' book.
		 
		
		
		
		
		
		
		
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