So True about the problem scope.
Even when dealing with just USA coins there some "gotchya's" involved.
The metal composition of the coins has changed over the years.
There are actually 3 different USA pennies. 1943, 1982 to now and all the rest.
I'm wondering if a 1943 penny would even make it through the magnets without
getting stuck to one.
There are multiple dimes but for modern dimes it is pre 1965 and post 1965.
Quarters also changed in 1965.
--- bill