How accurate are population reports?

[FrankWakefield]

I used to just throw away the slips when I busted slabbed cards out of the holders. But after a few years of that I started saving the slips, most of the time. I haven't sent them in, just held them... With me doing that a few dozen times, and with other contrarians like me doing it, it would add up. Add to that the crossovers, I'd think the pop reports are somewhat accurate, but not absolute. A bit diluted, still of some meaning and merit.

One aspect that is sometimes not considered is that some cards are more likely to be graded than others.... HOFers in T206 more so than commons, 460 series cards are slightly more likely to be graded than series 150 cards, eg for just T206.