>Undocumented components can prevent games from running at all (see how it took decades for >Raiden II to be supported due to the hardware using a custom chip for calculating bullet >trajectories)
Credits to Seibu's engineering team designing hardware protection very challenging for bootleggers to bootleg so Seibu themselves were also locked out of their own house.
Props to OG, Kale, various pcb owners that were testing Kale's code patches on their own pcbs and replying with feedback with the test results which eventually got Raiden II finally playable. Seibu Cup Soccer is probably the last of that era of games with protection yet to be fully worked out.