If you do a search and look thru old posts, I believe that the best info. is that the Model 500 Duke has always been stainless. In the 2000 catalog all 500 series are listed as stainless. In the 2002 catalog, the 501/503/505 are listed as stainless (500 had been discontinued). In the 2003 catalog, the 501/503/505 are listed as nickel silver. In one of the threads, it states that the tooling was changed as part of the material change. The angle of the seam between the bolsters and the birchwood are mirror image on the newer NS models. On the older SS models, there are different angles on the head and tail bolsters (also part of the design change). By the time the switch was made to nickel silver, the 500 was out or on the way out, so it was not updated.