https://www.psacard.com/pop/baseball...52/topps/49722
The PSA Pop Report will answer many questions for you.
In this case, the Gerald Staley cards have over 500 graded, with a total of 20 graded PSA 8 and only one 8.5. There are also a few 8s with qualifiers, making them approximately 6s.
You can look at the rest of the pop report to see which cards have zero 9s and 10s to find the ones that are hard to find in solid condition and centered.
Edit: and for what it's worth, it's possible the 8s don't ever come up for sale. However, if someone bought this thinking it was a candidate for a bump, they're going to lose on it. Despite having a hologram flip, the serial # is and old one, so it wasn't recently called an 8. With the top two corners showing significant wear to my eye, I'd be surprised if this would get a 6.5 today.
PPS: PSA breaks apart the black backs from the ones that are supposedly red backs, but it's likely that many without a designation may also be black backs that just haven't been sent in for reholdering since they started making the distinction. Anyone know when PSA started separating red and black backs in 1952 Topps?