Hey Phil, sure, no problem.
USA was added to the Deer Park slides when we changed the material from 17-4ph to 416 Stainless Steel. Then, the last updating we did was coded with the dots in USA (U.S.A.) This documented to us on "The Inside" that that slide had the firing pin hole moved approximately .150" to the right to fully center the firing pin on a round. It works fine the way it was, but Karl was being "A Putz" and he wanted everything to be right on, hence that update to the slide and the addition of those periods in between the letters U.S.A.
That was the last update prior to selling the company to Remington Arms.