Quote:
PCGS CoinFacts state that professional certification is essential.



... A few days ago, I read an article about a 1901-S quarter in the journal of the Liberty Seated Collectors' Club. The quarter was certified genuine by PCGS. The article's author proved the coin to be a fake. While certification sells, but it isn't necessarily the end-all.
Having owned a dozen or so, my guess is this '16-D is genuine. An expert's guess could "prove" me right or wrong! Good luck!
@grr601: A final thought ... Take the trio of Mercuries to a major show, and solicit some "coins-in-hand" dealer opinions, prior to submission.