Although described in the literature as "regular dies trial pieces", these are actually restrikes deliberately made in the early 1870s and sold as part of complete off-metal sets of the silver coinage of this year containing quarter, half dollar and dollar which had the reverses of 1866 with the motto "In God We Trust" above the eagle.
These three cent dies were made from a hub which had the "D" in "United" broken and may be a backdated novodel.
Examples were struck as follows:
Copper J375/P443 with about a dozen known, six of which are ex Edgar Adams, Elder 4/1935 lots 1388-93.
Photo courtesy of Ira & Larry Goldberg's Coins & Collectibles.
Aluminum J376/P444 with fewer than 3 confirmed.
Nickel J377/P445 with only 2 believed to exist, one of which is illustrated below. One was part of an 1864 nickel proof set which is ex Doughty (1891), H.P. Smith (1906), Brand (journal #33871).
Photo courtesy of Heritage.