I thought IREM themselves did the HuCard version and the CD version since the game runs in the higher resolution that IREM games tend to have and that Hudson games never seem to have.
Me too, to be honest. I don't have the HuCard handy to check, but I'll take Paul's word that Hudson is credited. Maybe Hudson had no part in the CD version at all. And maybe Hudson's role in the HuCard version was minor to begin with. Perhaps Irem really DID do the port themselves, but Hudson just released/published it. This would actually make sense. If you notice, when you boot the cart, you go straight to the title screen. When you boot the CD version, you first get the "Irem" logo splash screen before anything else. This screen is present on all the Irem games I've played on the TG except the R-Type cart.
I wanted to ask about that high resolution, actually. Is Irem the only company that utilized it? As mentioned, it seems most all Irem games use it. Why didn't more games use it? Were there restrictions it imposed that using the "normal" resolution didn't? Were you still able to use as many colors on screen at the higher resolution?