Is there a historic prescedent for sercet pardons? Have they occured before?

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2. Couldn't find anything federal, but in South Dakota,

Apparently there was a law that allowed a pardon to expunge all records, including the pardon itself, so it could be done in secret.

But that doesn't apply to federal pardons, there's no comparable law, and in any event that's probably a different scenario than most people think when they think of secret pardons. At least, I think of a president secretly delivering a pardon letter to someone who just puts it in a safe until needed.

No precedent from what I can find.