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.
Examples were struck as follows:
Copper J718/P799 with about a half dozen known.
Aluminum J719/P800 with about a half dozen known.
Nickel J720/P801 with about 3 or 4 known.
Photo courtesy of Bowers and Merena.