Although described as regular dies trial pieces, these were deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J1383. This is unlisted in Pollock. If any do exist, they are probably masquerading as a regular issue proof.
Aluminum J1384/P1528 with only 2 or 3 examples are believed to exist, including the illustrated example.
Photo courtesy of Heritage.