I was right--those two cards in question from the last post are not part of the Topps Sketch Card series. One (the B&W) is by artist Monty Sheldon and is part of a sequentially numbered series of 25 sketch cards, each 1 of 1. The full color one is described as an "artist proof" that Topps lets the artists keep. Personally, I think it was a card that Topps rejected in favor of another card from the artist. That brings our count back to 7. Fortunately, another one cropped up to bring our count up to 8.
Sadly, this card is quite similar to a handful of the others out there.