Although these are described as regular die trial pieces in the standard references, these were deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J739/P820 with about a half dozen known.
Aluminum J740/P821 with about a half dozen known.
Nickel J741/P822 with only the Newcomer, Lohr, B/M 2009 ANA sale believed to exist.
Photo courtesy of Heritage.