Dragon's Curse

Dragon's Curse is a Hudson-licensed port of Wonder Boy III: The Dragon's Trap (also known as Monster World II). For some impenetrable reason, it was dubbed Adventure Island in Japan, which was also the name Hudson used for their earlier Wonder Boy port, which spawned a series of games otherwise unrelated to the Wonder Boy/Monster World series.

Don't worry about it.

Debug Passwords
A couple of hardcoded passwords exist in the game which were likely used for debugging. Due to the rearrangement of password values between versions (both games skip I, O and Q, but they differ on the inclusion of F and S), the codes are rendered as nonsense in the American version, though they still function as expected. The Japanese game also spaces out its passwords.

Regional Differences
As noted in the intro, the histories of the Wonder Boy, Monster World and Adventure Island series are an intertwining mess. The original Adventure Island was a port of Wonder Boy, but the later games were almost all Hudson originals based on the style of the first. Conversely, the Wonder Boy series incorporated a variety of RPG elements and morphed into the Monster World series. Despite the major changes, Hudson continued to license the games for release on its own platforms and when this game's turn came, it was released in Japan as simply Adventure Island. Besides this difference, the title screens are almost entirely unrelated.