Although these are described as regular die trial pieces in the standard references, it is more likely that these were deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows.
Copper J1416/P1559 with at least 3 known.
Aluminum J1417/P1560 with only 2 believed known including:
1) B/R 9/75, Heritage 8/08 ANA, B/M 8/10 as NGC63, Heritage 1/18 FUN - PCGS63, illustrated below
Photos courtesy of Heritage.