The Natsume logo is still in Solbrain's ROM though, even if its not displayed anywhere (or maybe it's just in the ending?). and there are a few differences between the same graphics bank in Solbrain and Shatterhand, SFIV's version seems to be based on Solbrain.
btw i noticed some odd things in Shatterhand/Solbrain while I was looking into this. in the US version there are complete small and medium sized Natsume logos in that graphics bank, as well as a huge one in the next, none of which are used anywhere in the game. in the Japanese version most of the medium and one letter of the small is overwritten with graphics for the "area complete" screen from the fairground level (its more generic in the US version) but parts of the logos still remain. which seems to indicate the US version came first after all, and it only had the Solbrain licensed tacked onto it for the Japanese release. but anyway. thats nothing to do with pirates. so yeah!
back on topic (ish), personally I always thought it was strange that Final Fight 3 is based on the US version, for the same reason. And the US beta, at that. Same goes for Donkey Kong Country 4, only without the beta part.