Never knew about the missing Hudson releases though! Anyone know what they were?
Unreleased sequels to China Warrior (The Kung Fu). Hudson planned on releasing a new "chapter" every month over the course of a year. Upon completing a chapter, you would be given a special password that would allow you to continue with your health, score, and storyline (yes, an elaborate storyline was planned, with a story arc that spanned the entire series, punctuated by cliffhangers at the end of each chapter). At several key points in the story, you'd have the the opportunity to choose how to proceed -- this was intended to add replay value (i.e. folks would be curious and try to find all the different paths the storyline takes, not unlike a "Choose Your Own Adventure" book).
According to gossip in the Japanese gaming magazines, the Kung Fu series was cancelled when a project manager insisted that a Blodia / Timeball mini-game be incorporated into game.