I both agree mostly and disagree in part with all comments so far which pretty much are spot on. I tend only to operate in high grade and so look at these a lot [not Mantle though since he sucked and his cards are overrated
].
-I also follow the term 'fish eye' for them, but 'bullseye' works just as well
-they are ubiquitous, even in 9s, and if not the high-end pops of this era would be far lower than they already are
-I personally dislike them and avoid them as much as possible, even considering the eye appeal above corners and centering as so many others prefer to focus attention--just matter of personal opinion.
-they are not recurring, like some of the colored marks referenced, as in over and over in the same spot, but rather are utterly random, coming from air or bubbles or something in the process that is not fixed.
-any year with large swaths of color in the design (usually where the name/team are printed) seem especially susceptible
-PSA had an official statement on the site at one point (which I can't find now as it seems they've revised those pages a bit at some point) of how they review them and I recall they explicitly said it is a subjective decision based on eye appeal, so that if it were a big bad one smack on the face, that would be more of a downgrading issue than off on the side where '[it doesn't take away from the overall appeal]'