Although these are described as regular die trial pieces in the standard references, it is more likely that the off-metal 'trials' of this year were deliberately struck for sale to collectors in complete sets.
Examples were also struck as follows:
Copper J1365/P1510 with only 2 or 3 known.
Aluminum J1366/P1511 with only 2 confirmed including the illustrated example offered in a Holabird-Kagin auction and the other in the Harry W. Bass Jr Research Foundation.
Photo courtesy of PCGS.