That's not exactly true. If you read their book it tells you that to get the 70 grade there can be no flaws or hairlines visible at 5x magnification.
As we all know, the 2 primary TPGs are PCGS and NGC. PCGS promotes a concept called First Strike, connoting a coin was struck early in the life of a particular die. As we all know and unless things have changed recently, when a particular coin was struck cannot be known. Likewise, NGC promotes concepts called First Releases and Early Releases. This can be known, but who cares when a coin was released as it basically means nothing. It has nothing to do with when it was struck. When we get to the point where we fully appreciate the fact that the above concepts are merely BS, we will begin to appreciate how much credibility the TPGs deserve in general, which is very little. Grading is a game and a money grab, especially in the arena of modern coins and bullion. It may, however, hold some value in the realm of the non-modern. It's only my opinion, but the game these days is inflated and out-of-control. The party is going strong, but it will someday come crashing down like a house of cards.