Regarding PSA pop reports: I think that PSA understates BL460s because for some reason they didn't distinguish between 350s and 460s in their pop reports for some time. I began a thread in 2013 about why there were only 350s in their pop reports. It turns out that PSA separated them on flips into 1910s and 1911s, but listed them all in the pop reports as BL350s.
I don't know when they broke out 460s as a separate group. I also don't know if they went back and corrected their pop reports, or only listed BL460s going forward from that point. If they only listed them going forward from the time they separated them in the reports, that would cause the numbers to be under reported.
I'm bad with links, so I'll just bump that old thread to the front page.
