There's a clawback provision in place in most major auction house contracts that states that the funds for any sold item (or the item itself) can, at any point

There's a clawback provision in place in most major auction house contracts that states that the funds for any sold item (or the item itself) can, at any point in the future, be recouped from the buyer/seller if proven to have been stolen or fraudulent. Basically as the seller of such an item you'll be sued, so be sure proof of provenance is sound. In this case the letter was part of a government archive, so back to Massachusetts it will go...