Although described as a regular dies trial piece in the literature, it is more likely that this was deliberately struck for sale to a collector. In copper, as illustrated above, only 4 or 5 are believed to exist.
It is important to note that the genuineness of some of these copper pieces has been questioned in the past.
These were also struck in silver J281/P332 as shown below.
As the 3 known examples are actually business strikes, struck on dime planchets and not proofs, it is likely that these are really mint errors.
Photos are courtesy of Heritage.