A search yields this result:
https://basicroleplaying.org/topic/956-magic-world/"Magic World could be a part of the Empire of Tzand included in Perrin's North Coast campaign and neighbouring Illyrion."
Both Magic World & RuneQuest are part of the Basic Roleplaying System, so I'm not sure if Magic World would have been considered a different system to Perrin when he made the remarks at:
Steve Perrin Interview"My original dungeons do provide the framework for my North Coast campaign, which has been used for at least five different game systems."
If Perrin did consider Magic World a different system than RuneQuest, then were Future World & Superworld different systems too? Did either of these components to the Worlds of Wonder box include "North Coast" as a campaign setting, perhaps at different periods of its history? If so, that would add up to five systems.
Sorry I don't simply know the answer. I attempted to trade for a friend's copy of Worlds of Wonder once about 20 years ago, but he wanted to hang onto it. However, I could not resist the nerd/hipster intersectionality of the Superworld scenario "Bad Medicine for Dr. Drugs," so I will check my copy when I get a chance.
