Look at the pops of the 69 's and the 70's and consider this. As cheap as the 69's are, no one is going to send in indivudual coins unless they really believe they are 70's. (OK some will be from bulk shipments) So figure just a quarter of the coins sent in are non-bulk shipments. So divide the number of 70's by 1/4 of the total submissions and multiply by 100. The answer is the percentage of the "I'm sure it's a 70" coins that you send in that will actually come back as 70's. And remember that is what you get back if you are just sending in the cream of the crop. (By selecting 1/4 I'm being generous. If the fraction is larger then you get back an even smaller percentage.)