https://e621.net/wiki_pages/5343 shows that butterfly position will automatically be changed to piledriver position

I've seen them described as different things on VNDB though:

piledriver https://vndb.org/i1696 "receiving partner lies on their head and upper body with their legs and hips up, while the penetrating partner stands above"

butterfly https://vndb.org/i1699 "receiving partner lies down, face up, while the penetrating partner kneels, squats or stands in front of them with their torso mostly upright. The receiving partner may have their hips raised up or rotated slightly penetrating partner may kneel or stand on a lower surface than the receiver so that they are not too high up"

Basically a piledriver is predominantly stacked-up to a much greater degree than one sees in butterfly.