We don't know if there is more than one of these. If this is a true one of a kind error coin I would not be in a hurry to sell for the first offer.
I believe there is only the one.
I also text a photo of the batch this came from to Minerjones, who was collecting these to ship on others behalf. I noticed the mistake as highlighted here:
https://i.imgur.com/iPPDSpf.jpgI have a process in place with the keys, where I triple-check that the public and private keys are matched and printed correctly, and that they match their respective serial number. With all of my attention on this critical detail, I believe I overlooked that the coin was placed inside the housing incorrectly. After drilling, I also passed these off to an assistant to clean and polish... had I been the one to clean them I surely would have noticed this. When it was handed back to me, I checked for a fourth time that the serial matched my printed list of public keys before packing, so like I was saying, my attention was focused on the key and the serial.