Contemporaneous means that you have to have received it by the earlier of the date you file your return or the due date for the return, including extensions.

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And you need to have the substantiation letter from the charity on or before the earlier of the date you file your return or the due date (including extensions) for filing the return.

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For purposes of claiming a refund, the SOL expires three (3) years from the due date of the return even if you file the return before the due date.

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The FDIC has three years for tort claims and six years for breach-of-contract claims to file suit from bank closure date.

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You can amend past returns and file for back refunds for up to three years from the original due date of a return, including extensions.

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Each tweet is a JSON file, containing an immense amount of metadata in addition to the contents of the tweet itself: date and time, number of followers, account creation date, geodata, and so on.

FORBES: The Library of Congress' Twitter Archive, One Year Later