Only the Base Set has Thick and 3D stamps, and most 1st edition stamp variations.
All other sets are always Thin, but it is indeed possible to have a Grey Thin stamp. I’ve got a Neo Genesis Pikachu with a Grey stamp, and I’ve also seen a bunch of Gym Heroes 1st edition cards with a Grey stamp before.
Apart from that there is of course the “d” edition error for the Jungle Butterfree.
PS: All this is also mentioned in my article. 
Greetz,
Quuador