I believe all the stainless frames started with an S, and the armor alloy frames started with an A on the serial numbers. I would need to dig mine out to check, but I am sure others would know for sure.
Is the cougar a full cougar or just a cougar's head? Is the hammer, selector, trigger, trigger guard, and hinge pin stainless/silver? I have the silver Duracoat finish on one of my frames and several barrels and french grey on a previous barrel, and they are slightly different in color to stainless. I really like the finish and don't have much of anything blue anymore, and use a matte black on the others.