They are not accurate at all for any coin where there are significant price differences between individual grades, especially at the high end. There are some rare proof and circulation issues where the certified populations exceed the total mintage....and that's knowing that only a fraction of that total mintage was even sent in.
Some big time dealers that are sending in massive amounts of coins and thus get huge discounts and free submissions etc. are driving this. If they have a certified coin that is worth, say, 10,000 currently, but goes up to 30,000 one grade higher, I've known of situations where one coin has been sent in over 20 times.
Some big time dealers that are sending in massive amounts of coins and thus get huge discounts and free submissions etc. are driving this. If they have a certified coin that is worth, say, 10,000 currently, but goes up to 30,000 one grade higher, I've known of situations where one coin has been sent in over 20 times.



















