I'm not a merc expert, but are there any die markers on the small bit showing that could have been used to date the coin?
That's a good question! One would think it unlikely for sufficient markers to be known on such a small area for a coin with such a large mintage produced by who-knows how many die pair, but I suppose stranger things have happened.
I agree it's unlikely. With some series you can identify a die with the *right* area that small though. If the die was only in use for one year, there's your date.
Indeed, or even in others where there's only a few pairings it would seem more reasonable. With a coin with what, 20+ million minted it's just hard to believe.
But if just some of those were minted with one die pair that does have an unmistakable mark in just the right spot, you might get lucky. Or, PCGS might goof.
Of course, but what are the chances? Unless there's some easily identifiable known anomaly attributable to a single due used, I'm unaware of anyone (including the almighty) having nailed down the die pairing for the entire run of 1916 Mercs. All things considered, I'd bet on your second possibility.