Although described as regular dies trial pieces, these were actually deliberately struck for sale to collectors as part complete of a copper set. 3 sets were known including the one in the Garrett collection that was sold by Stacks in 1976 and a double set was apparently stolen from the Iowa State Historical Museum.
About a half dozen are known.
Photo is a colorized regular issue shown to approximate what the die trial would look like. Photo used is courtesy of Heritage.