It is exceptionally difficult to reverse a one-way process and create from it the die (including appropriate degrees of die-wear) used for striking a coin.
This is actually good for us. High end fakes can inevitably be unmasked if enough effort is applied.
To
help those who don't fully understand this point, I show below three examples of this "logical inconsistency" problem from my
plated coins webpage: http://andrewmccabe.ancients.info/Plated.html
The above two coins cannot, logically, have been struck from the same
reverse dies because of the border-dot mismatch between 7pm and 9pm, yet the dies are otherwise identical. Hence the lower coin is a
fake produced by
hubbing an example of the upper coin. It is logically impossible for them to have been struck from the same dies.
The above two coins cannot, logically, have been struck from the same
obverse dies, because the lower coin has a die-break at the bottom of the left-lowest hair lock that is not present on the upper coin, and the upper coin has die-breaks, for example at the front of the neck truncation, not present on the lower coin. It is logically impossible for them to have been struck from the same dies.
The above picture shows a die (top) and a coin (bottom) but the coin cannot have been struck from the die, despite them appearing identical, because the die lacks details of the fringe-hair that are present on the coin (i.e. the die was made by
hubbing a worn coin). Again, logically impossible for the coin to have been struck from this die.
Although all these examples relate to
plated ancient
forgeries, the technique in proving logical-impossibilities is in principle the same when determining whether any two coins are struck from the same dies. The more examples are known from these dies, the more difficult it becomes to make a die that side-steps all possible logical impossibilities.