Yes this is a novel by Poe."18--", if this is a novel, means that the author doesn't want to set the exact year of the events.
Well, in America, it would be 7/10/18--. I generally recommend against that type of nomenclature, because it's not internationally valid. 10th July, 18--, 10 Jul 18--, July 10, 18-- are all unambiguous.So, it is 10/7/18--.
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