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 J672. This is unlisted in Pollock. If any do exist, they are probably masquerading as a regular issue proof.
Nickel J673/P749 with only one or 2 believed to exist.
Aluminum J674/P750 with about a half dozen believed to exist with the former J.E. Drew example illustrated above.
Silver-copper J674A/P751 which was supposedly struck from native Michigan ore. It is unique and is ex Johnson (Nov 1898), Hall, Brand (journal #49986:115), Boyd (per B.G. Johnson 7/16/41 invoice), Kagin 7/78, J.E. Drew, Simpson collection - PCGS61 and is illustrated below.
The earlier pedigree is from Dr Hall's collection notebook on the Newman Numismatic Portal and is shown below.