Although described as regular dies trial pieces, these wee actually deliberately struck for sale to collectors as part of complete off-metal sets.
Examples were struck as follows:
Copper J678/P757 with about a half dozen known.
Aluminum J679/P758 with about a half dozen known.
Note: There is also an example in nickel which is described as being struck on a broad planchet. It appears in several Kagin's sales in the 1970s and was illustrated in their July 1975. It is not known if it is just a broadstruck mint error or a some kind of die trial.
Photo courtesy of PCGS.