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Marc S.as it is singular in nature, to the best of my knowledge:
That said, I have an Allegheny, which is unique. And I also have two versions of an uncatalogued E104-III (e.g blank back and Nadja back). Now, the card is uncatalogued, which I think definitivel makes it rare, even by E104-III standards. But I also know of four examples of the card, so definitely not on the order of unique. Only one of the four, I believe, has the Nadja back, though.