never seen a layer of copper under nickel on a skillet, like you might on an item that has been "triple-plated" with chromium (copper, nickel, and chrome).
I have a Griswold 10 Button "bright chrome" skillet cover that was in fairly nasty condition. I had it stripped. When I picked it up, it looked pretty good, but when I lyed and cleaning it, a copper tinge was clearly visible. I am convinced that Griswold bright chrome from the 30's forward included at least some pieces that were triple-plated.
I know some earlier pieces were tin-plated, and I understand that tin is not as tightly bound to the iron as copper-nickel-chrome. There may also be pieces that were chrome-plated without the use of copper.
PS the company that did the stripping was unsympathetic to my dissatisfaction, and did not care that I would not go back to them. Try this on low value pieces first, not pieces that you will unhappy with your investment on, if it does not turn out well.