Although these are described as regular die trial pieces in the standard references, it is more likely they were deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J1173/P1315 with about a half dozen known.
Aluminum J1174/P1316 with fewer than 3 confirmed.
Nickel J1175/P1317 with only the Woodin-1914 ANS exhibit, Newcomer, Farouk, Pine Tree 9/74, Paramount 4/77 example believed to exist.
Photo courtesy of Heritage.