Posthumous

Posthumous use can refer to:
 * a stamp used after it has been invalidated.
 * a cancel used after the time it was invalidated.

While (say) old canceling devices are brought back out for use in an emergency, those, if proveable, are legitimate usages. Still, old stamps and canceling devices are around and can be used by forgers to create legitimate-looking items like stamps that are scarcer used, and also covers. Dating by reference material or submission to experts will reveal those items to be forged.

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