You've got a good point

To respond to "audrop". Good observation. I've done the deed that you are talking about. In defense of the double sets. I record/ register 2 Canada Pl quarter sets. I do this for two reasons. First, the value of some of these, I feel should be secured. By photo, and registry, if something happened, like fire, or theft. I would be able to claim these with insurance easier. Secondly, I really want a top NGC set. However, sometimes I can only find PCGS slabbed coins. Now, I actually two sets going, hopfully eventually, to be able to separate them into a PCGS and an NGC set. I do believe in what you say about those who only register PCGS coins. I don't know if I am envious of their complete sets, but, for sure, it seems a little strange to value the NGC registry with PCGS coins.