Did you keep a copy of the serial numbers? Or a photo of the framed article, which might show the serail numbers? Given that they are going up in value, I would suggest you keep an eye out on ebay and auction catalogues. I don't know the law in the US, but in Australia you still own the item and claim it back if you happen to see it. The person who currently has the note/s has to give them back, regardless og how they came about them, legitamately or otherwise. I don't believe the is a statute of limitations either.