There's more to it than just identifying the flow lines though. But even if flow lines were the only thing involved, there would still be differences because of the very nature of flow lines. Because the metal flows across the surfaces of the die it wears on the die with each strike. So even though 2 successive coins will be similar, they will not be identical. The process also identifies and records even the most minute contact mark and all strike characteristics. Think about it, contact marks - from the first coins ever struck in the 1700's to those of today, when the coin leaves the press it is tossed into a pile or into a hopper. And every subsequent coin lands on those previous coins. That causes contact marks on every coin. Then there is all of the other possible contacts from handling, like counting and sorting and bagging and distribution. Every single coin goes through this and always has. And that's just for the MS coins. Coins that have seen circulation have even more differences. Then there are strike characteristics. Every coin struck is unique in this regard alone, let alone the others. For with every strike there is a multitude of things that can change. The planchet can be a tiny bit thicker on one side or the other. Or this planchet will be slightly thicker or thinner than that planchet. The strike pressure will vary slightly. The dies can move or shift slightly in the press between strikes. The dies can bounce upon strike. And wear will cause one particular spot on the coin be struck up better than on another coin. So between these 3 things it is impossible for any 2 coins to be identical. Just like a human's fingerprints are 100% unique, every single coin is also 100% unique. That's why the process works, and that's why they have had a 100% success rate.
So what is the enforcement procedure with the doctoring of coins? A submitter is found to be sending in coins for grading to PCGS or NGC (presumably ANACS, etc. are not market acceptable enough to be used). The owners of the TPGs become aware of the situation. They can go back as far as they want with an audit/examination of the account for this fraud like the IRS may do if they detect fraud. Once they have ascertained the level of the fraud, they will probably speak to their lawyers about their options with the submitter/dealer. All coins that have then been certified for the submitter/dealer can easily be identified in the marketplace unless they have been cracked out or reholdered. Do those who are aware of the doctoring have a responsibility to report the fraud, as with other crimes?
There really is no enforcement per se. PCGS filed a civil suit against several of the coin doctors, the suit got dismissed if memory serves. Other than that about all that can be done is for the TPGs to refuse to accept submissions from the doctors and for the ANA or other numismatic associations to kick them out of the clubs. There is no law against doctoring coins so nothing else can be done.
I checked my latest copy of "The Numismatist" and it looks like only one person was given the boot this month, a person who had been convicted of grand larceny, the ANA got wind of it, so she was given the olde heave ho. I think I also saw Bob Bruce's name on the list a while back. If memory serves he was big on the gold Norse coins peddling them for well over $10K. Probably a customer wised up to being ripped off, and then tried to get some justice through the regulatory machinery of the ANA. You usually have better luck with a lawyer. I heard one dealer complaining how another trusted dealer robbed coins from him and others. They decided not to get law enforcement involved since it was one person's word against another's.
