As far as I can tell, it's a standard pistol throughout. The finish is outstanding, but that's the way they were made back then. Very smooth and deeply blued. Perhaps extra care was taken in hand-fitting the components? It remains a mystery to me. It was bought new, directly from a dealer, but the dealer was strange. I was taken to him by two co-workers, who had bought PPK/S's from him, and his "shop" was not the standard gun shop. It was a back room sort of set-up, but he did have a firearms license and we went through all the paperwork. That was in about 1972, before firearms laws and regulations were tightened. I don't recall the dealer's nationality, but he spoke with an accent and was from Russia, or other USSR member, originally. It was kind of a spooky experience, really. Out in one of the boroughs of NYC. My co-workers and I were FBI agents, so it is doubtful there was anything illegal involved. I didn't notice the "Premium" aspect until well after the purchase. I wish now I had questioned the seller about it. There was nothing extraordinary about the price. I guess it will remain a mystery.