The introduction of third-party grading services had a tremendous impact on the numismatic hobby and marketplace. With the advent of PCGS in 1986 and NGC in 1987, coin grading became significantly more uniform and precise. In the short-term, third-party grading immediately brought trust, consistency and liquidity to the numismatic market. In the long term, meanwhile, the grading services also helped numismatists understand the true rarity of coins.

Since inception, PCGS and NGC have maintained records of every coin they have graded. This data, collectively known as the population reports, has become increasingly valuable over the years. In the late 1980s, when third-party coin grading was still quite new, only a small percentage of all valuable coins had been certified by PCGS or NGC. Therefore the population reports reflected just a small sample of all coins in the marketplace.

Since then, the grading services have seen tens of millions of coins—if not the majority of $1000+ items to hit the marketplace. In addition numerous major collections have hit the auction block, such as the Norweb, Trompeter, Eliasberg, Pittman, Bass, Newman and Pogue holdings. These collections were formed before the era of third-party grading, but since being offered for sale, virtually all of these coins have been graded by PCGS or NGC. This data helped round out the population statistics.

While the population reports have become much more accurate and insightful over the years, they are not perfect. Even though the vast majority of valuable coins have been seen by PCGS and NGC, there are still important rarities surfacing every day. Previously unheard-of items are still being discovered on a regular basis. Furthermore, the stats have been slightly inflated due to resubmissions. If a coin is cracked out of its PCGS/NGC holder and resubmitted, the coin will appear twice in the population reports unless the old certificate is turned in. The grading services have taken steps to remove obvious duplication, but it’s impossible to fix this issue entirely.

Not only have the population reports helped determine rarity levels, but they have also made certain coins even more desirable. A new market has developed for “top pop” coins, i.e. those that are the finest on record with none graded higher. Determining “finest known” status for a given coin was once highly subjective, but now collectors can refer back to the population reports. If a coin is the single highest graded by PCGS and NGC, it is generally regarded as the finest available specimen (and rewarded accordingly in terms of value).