The determination of what is a modern counterfeit and what is genuine, is pretty easy to determine if you have even to slightest knowledge of 8R coins and their counterfeit markers.
Determining a contemporary counterfeit from a genuine 8R is still a very inexact science. For every person that will tell you why a coin is genuine, there is a person that will tell you why it is a counterfeit.
Metal analysis seems to be the way to go , but even that has come under scrutiny. Just ask swamperbob how many times he has had to edit his book due to new developments in the field. Since many old coins were melted and restruck, many people say that only 20% (if I remember correctly ?) of all 8R coins may actually be genuine.