Really nice find! The best error card in my opinion, and one of the rarest, if not the rarest. I’ve heard conflicting stories. I heard from a few sources that it was included in the very first Shadowless Brushfire theme decks. But I’ve also heard from sources that it was included in early Shadowless packs. Therefore we’re basically at square one lol, or it was in both. The one thing we know conclusively is that it was included in the earliest prints then revised.
That was my hunch too, but a hunch is still a hunch.
There is no way to put a # on how many. But we do know there’s lots of demand and little supply for them. Someone got a figure for the dark dragonite error from Wotc but it will never happen again.