I was able to nab another, one of one, printing plate of Herschel, for the Hoard. This is the Yellow plate, from the 2018 National Treasures Collegiate set #13. There are two different poses of Walker in this run. #13 cards feature him in a more straight ahead running pose, while the #33 cards picture him in more of a side view.
Obtaining this card give me a full, four card run of Printing Plates in the #13 run. Black, Magenta, Cyan and now, Yellow.
The funny thing about this purchase, is that the seller was advertising it as a Black Printing Plate. I already had the other three in my collection, so I figured that he just didn't know what he had. This is the first time I've ever been able to get all four plates which are avaliable.
As far as the #33 plates, I have the Black and Yellow, but lack the Cyan and Magenta.