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That was also a possibility suggest by the experts, that someone with the required skills altered the coin.
I think if that was the case this coin would of never been lost, but instead been sold as a new error coin, but when it comes to something like a date error coin that is in circulation, or most all error coins there is never just one made before the error is discovered.
If someone with the skills and knowledge to produce a fake error did this they would of made more than one and there would be others out there, even if they were acknowledged as fakes.