Using population reports to check a seller's claim
"One of only three" is a checkable statement. The grader publishes the number.
What a population report tells you
A population report is the grader's count of every copy of a card it has graded, broken out by grade. If a listing claims a card is one of a handful at that grade, the report either supports it or does not.
It also gives you the shape of the market: a grade with a population of thousands is not scarce, whatever the listing says, and a price built on scarcity should be questioned when the scarcity is not there.
The limits, stated plainly
Population counts only what has been submitted and graded. Cards sitting ungraded in collections are not in it, so a report is a floor on how many exist, never a ceiling.
Counts also move. Cards are resubmitted, crossed over between graders, and occasionally removed. A screenshot of a population from two years ago is a historical figure, not a current one.
Cross-grader counts
The same card graded by four companies appears in four separate reports. A claim about total scarcity has to account for all of them, and no single grader's report answers it alone.
Verify it yourself
FLOAT prices collectibles from realized sales. A valuation assumes the item is what its label says — which is why these checks come first.