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 J1023/P1158 with only 4 or 5 believed to exist.
Aluminum J1024/P1159 with only 2 or 3 believed to exist.
Nickel J1025/P1160 which is believed to unique.
Photo courtesy of Stacks.