Three of the 4 promos from 91 had been on my list for a long while. They had a limited production and while most Conlon prototypes or promos had a large back stamp indicating that status, these had no stamp and could only be distinguished from the regular set cards by the lack of a copyright line on the bottom back. A recent ebay auction allowed me to get the 3 I was missing but only by purchasing an uncut sheet with 6 copies of all 4 of the promos
https://www.ebay.com/itm/126532737488