Join the PCGS Registry. It's free and all you need is one PCGS Graded Kennedy in Business Strike and one in a Proof Strike and you can create literally ANY Kennedy Registry Set (usually Complete Variety Sets) then use the "What if" feature of the registry and view every Kennedy the PCGS attributes. You can even look at populations for each grade as well as PCGS prices.
PCGS's variety attribution charge was always pure bool shat since they just compare the coin with the limited pictures in the CPG. Sometimes they didn't even get that right. Basically, you tell them what it is (you did all the work and research) and they either agree or disagree for $24.
No doubt. These Kennedy Varieties can be very exciting to obtain. Even more exciting if you find them by cherry picking. As for rarity? That's a tough call since some can be quite common. Hard to locate but not impossible. Your excitement when finding these, is difficult to contain. I know mine was.