On the ZX Spectrum, there is a game entry for Jet Set Willy and another for Jet Set Willy II: The Final Frontier.
Some releases of Jet Set Willy II were released under the Jet Set Willy II name and some under the Jet Set Willy: The Final Frontier name.
Currently several of the releases under the original Jet Set Willly game are actually The Final Frontier and should be moved under the Jet Set Willy II game.