My understanding is that only one O27-E1 exists.
O27-E1 is a 1873 3c Justice Dept mock-up essay in black & gray. It is an artist's model prepared by Joseph Claxton.
It has a model of the engraved vignette, numeral and value label on yellowish card stock, which is mounted
on a pencil and wash drawing of a frame on white card stock, 90 x 118mm, and signed in pencil by Joseph Claxton.
The $10,000 catalog value is based on the most recent Bennett sale