OH WOW!!Nice reverse mirror die cap . It happens when a planchet is struck and then sticks to the hammer die(Die cap)which results in the memorial side becomes the die and striking the next planchet with the results you have.Congrats on a nice find
Brockage error! I have found 2 on eBay you could probably get like $75 for it maybe a little more. I took my two into a coin shop and they offered me like $35 or something for it. I turned it down my 2 look just like yours.