Interesting, thanks.
I suppose standard government minted coins are not bad because at least there are physical features and published weights for the coins, and a bad counterfeit (in terms of weight) would be detectable unless the counterfeiter had good method of combining cheaper alloys and plating with gold.
Kind of depends upon how frequently the “assessor” (aka the potential buyer) sees the items in question. As time goes on, the Chinese have gotten better and better at counterfeiting (first) US silver dollars, then silver eagles. Eagles, as you may or may not know, have some very fine details and of course, do not circulate as currency, so they are almost always in choice, top-notch condition. Hence, those details are intact. OTOH, old silver dollars were produced in ASTRONOMICAL quantities and many DID circulate (and many were held in dresser drawers) There are crappy ones and choice ones. The danger for the unsavvy buyer IMO is in buying average condition silver dollars at attractive prices and getting glud. Why does this happen? Because the unsavvy buyer doesn’t eat & breathe silver dollars every day.
So...silver dollars. OK, most people have seen them but do they look at them every day, several times a day? On clumsy copies, sure, those can be easy to detect, but as time goes on, a potential buyer needs to be more and more and more familiar with teeny details and develop a “spidey sense” about what he/she is buying on these things. It’s like Democrats, they don’t care how many times they fail, they’ll just rework their dies and try again next month.