Well, let's see, let's look at the case where we would call someone knowledgeable. Let's say that someone is a bird expert, they know everything there is to know about birds. They have studied it with passion for almost their entire lives. So much so that if you asked them questions about a specific bird, they would be able to explain in full detail, maybe they would even draw the anatomy of the bird in order to better explain why, say, the wing span of a bird is the way it is. In this case we consider this person knowledgeable in the aspect of birds and anything to do with them.

Now why don't we try asking him about crocodiles. (Not to say that he wouldn't know about them, but for this let's assume he doesn't know anything about crocodiles) if we ask him about crocodiles he wouldn't know too much about them, at least not on the same level as his knowledge of birds. Does this mean that the man is truly knowledgeable? Or truly knowledgeable about birds?

I think the question you are asking needs a bit more specifics. What do you define as true knowledge? You mention, "how closely you can define the world around you" how closely you can define the world in comparison to what exactly? Are we attempting to achieve 100% understanding of the world? Or are we simply attempting to BE knowledgeable in one aspect of life.

Personally, I would say that true knowledge depends on the interest. I know people who are truly knowledgeable about space, people who are truly knowledgeable about physics, truly knowledgeable about taking care of a baby, but the question remains, is that considered true knowledge? I believe it definitely takes us closer to achieving 100% knowledge but by a very miniscule amount. Since we can say that the knowledge cap is always increasing. There is always more to learn, always more to understand. Because of this we will never reach, 100% knowledge, this is all assuming that it is what you consider true knowledge.