The guy who is the World Governments scientist( and the reason why the technology far from the 1500's) Vegapunk wrote the book. I do no think that they have clearly given a reason why they know what the fruit does but here are some hypothesis on it
1. They are fruit and from the way they look or features of them he was able to figure out thier properties as taste and ability
2. Maybe the cursed fruits evolve when ever a new one is made( every 30 years one of you said) , so from the newest fruit he found, he was able to trace the past fruit made.
3. He is such an unbelieavable genuis ( meaning ONE PIECE is being One piece) that he was able to discover every fruit and a pattern in them for the new ones to come. Come on he was able to make a cyborg before franky even had the idea. |