I've mentioned another possible variation before, but never really pushed it, because I thought it was just exclusive to certain backs...BUT there's two on ebay right now, that show the variation existing even among the same back.
http://cgi.ebay.com/1909-11-T206-PIE...item53e828934f
http://cgi.ebay.com/1909-1911-T206-O...item2c5d49b048
Both of these Wilson's have the Piedmont 350 back. While showing both variations in the red/orange burst in the background..
By that same thought, is this partial N exclusive to the Piedmont 150's, and is there complete N versions within the Piedmont 150's?