User blog comment:Otakon7/Otakon7's Buddyfight Simulator/@comment-29684437-20181105025046/@comment-36375292-20181105025659

As you can see from Otakon's reply to my comment, literally below yours, the cards are compiled in the sim with only 1 category.

So, when new cards enter the sim, for let's say... a dual card (like Zodiac who belongs in both Legend & Star Dragon World) that belongs to 2 worlds, seeing as the card will only be complied to one category, Zodiac will either end up in Legend or Star Dragon World.

It was done that way to include the cards that had no worlds.