While doing a Taito search in the Arcade Flyer Archive, I managed to find the original Japanese flyers for Darius. However, there's something very interesting about this one...
http://www.arcadeflyers.com/?page=flyer ... 70&image=3
http://www.arcadeflyers.com/?page=flyer ... 70&image=4
Look at the boss lineup on the bottom. Namely, two bosses who SHOULDN'T be there...Also, if I'm reading it correctly, some bosses were planned for much earlier stages (I wonder how you'd tone down Keen Bayonet for Zone C, though).
It looks like Super Darius was in part Taito's chance to implement the bosses it didn't have time to put into the arcade release...