This may be my last coin post for a while, we shall see, but I won't have my scope with me for close ups.
So, thinking about trying for a variety set? All the doubled dies from 1970-S? All the RPMs from 1960-D? All the 2009 DDRs? Well it's not so hard when you start, as there are always a bunch of strong ones that are either easy to spot while searching or someone has put one up for sale. But then they get harder, and lesser. Some are so trivial that few look for them, and even if they find them they have so little sale value that they don't take the time to try and sell them.
Here is one of the latter. It's a DDO-001 that I don't think I've ever seen for sale. It's extremely minor, just some light doubling on IN GOD and a bit under the LIB. Few know it's a thing, it probably can't be seen on most circulated coins, and no one is collecting them so who would bother to sell one?
1937-D Lincoln Wheat cent
doubled die - DDO-001