rasmith3442 I suspect that your 4566 was given a Melonite finish after it left S&W.
All my factory Melonite 4566s have an "M" on the factory label under the finish type. My stainless 4566s have an "S" on the label. As does yours. Also, I have never come across a Melonite 4566 with a forged hammer. All of mine and those I've seen have MIM hammers and triggers.
Yours is one rare and VERY nice 4566!
Best regards, 18DAI