I think this goes to show just how rigid the "only use assets from Sticker Star" thing was... they found a use for Paper Luigi that would only require his sprites from Sticker Star. The only modifications were separating the head and body so he could nod to the music. But you can tell they just cut the head off his SS sprite rather than had the version from before that was assembled, because the extra notch that normally goes behind the body isn't there.

I think any PM sprites in PJ that weren't in Sticker Star were simply cut things from Sticker Star that were removed from its data. Except where absolutely necessary (like the rackets from that Trio move) which are still just new assets added into Sticker Star assets, no assets were pulled from any other PM game, which means Paper Luigi was never going to have much more sprites than this.

To be fair they did say PL had been considered as a party member. But I think the decision to exclusively use assets from Sticker Star came after that.

yet again he only has this few sprites, sad, i guess the really didn't care about him