I have been corresponding about this with Robert, and I'm also eager to solve this mystery, so I contacted Yale to ask for more information. This is the reply I received:
The catalogue to the collection states that they date to c. 1880, in pen and ink, hand coloration. The catalogue entry reads further: 'Back plain. Square borders, square corners. Single figure trumps; copies of the standard trumps of the Marseille tarot.'
Personally, I'm a bit confused - the cards are obviously influenced by Wirth, but if they date back to 1880, then that would mean they actually PREDATE Wirth's deck, which was first published in 1889... right?
It would surprise me if they would turn out to be Wirth's original drawings, because the divinatory meanings written on the cards don't seem to be in line with what Wirth wrote about them in his Imagiers du Moyen-Age. (If anyone is interested in the translation of the divinatory meanings, let me know.)
Basically, I think it's very odd.
Any thoughts? Please correct me if I made a mistake, because I don't know nearly as much about Oswald Wirth as I'd like to.
Spoon