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 J1253/P1395 with only 2 to 4 known.
Aluminum J1254/P1396 with only 2 or 4 known.
Photo is the former Bass Foundation gilt example colored up and is courtesy of Superior.