So, an 1860 coin dug at a Rev. battlefield is fair game?
Bruce, are you referring to ARPA ? If so, that would only apply to federal lands. Not state, city, county, private, etc.... (unless drawn in by specific inclusion. Meaning, some state parks have equivalent cultural heritage verbage).
Or are you referring to coins not in an archaeological context ? If so, this has been a bone-on-contention and debate for a long time. Because there is wording in ARPA that, on the surface, makes it appear that coins and bullets are exempt. But a closer reading of that reveals that this is only true in-so-far as those "coins or bullets" are not found in an archaeological context. And you know full-well what some purist archie will say: That all their entire park or forest is "an archaeological site".
Naturally there is a good come-back for that (although it will probably fall on deaf ears): That there is a numerical designation system of archaeological sites:
https://en.wikipedia.org/wiki/Smithsonian_trinomial
So as you can see, for a site/spot to be "archaeological", it has to be designated as such. So what does that tell you? That obviously PRIOR to getting such a designation, it WASN'T an "archaeological site" (you can't have it both ways, eh ?). Hence your 1860 coin, found on federal land, yet outside of an archaeological site, would technically be exempt. But as I say, this will probably fall on deaf ears.
There's scores of coins being found, at federal sites, that are older than 50 yrs. old I betcha. And unless you were at Ghettysburg, Shiloh, or an obvious sensitive monument, parading yourself in front of bored rangers, then ... keep your math skills to yourself.