Although described as regular dies trial pieces, these were actually deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J1176/P1318 with fewer than a half dozen known.
Aluminum J1177/P1319 with only 2 or 3 known.
Nickel J1178/P1320 with only the former Farouk coin believed to exist.
Photo courtesy of American Numismatic Rarities.