Although described as regular dies trial pieces in the literature, these were actually deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J1087/P1223 with about a half dozen known.
Aluminum J1088/P1224 with fewer than 3 confirmed.
Nickel J1089/P1225 which is believed to be unique and ex Dunham, Farouk, Superior's 9/02, Simpson-Heritage 8/21 - PCGS64
Photo courtesy of Superior.