[swarmee]

There is a slight premium paid for PSA graded cards in new flips, but not nearly to the point of the additional premium for well-centered cards. It's kind of in the noise right now. However, the tougher PSA grading gets, the less cards that get high pops and the increased value on the current PSA 9 and 10s out there.
PSA told some people at the National that the 1955 Bowman Mantle they graded a 9 was the first to get a 9 in like 20 years. So part of it is that most Mint cards from 1960s and earlier are already graded. And people are less likely to break out PSA 7/8s of yesteryear to resubmit raw because they likely wouldn't get 7s or better again. That would lead to more cards being reviewed in PSA holders, and the pop report would reflect the changes because the same cert number would just be updated with a new grade.