You can look at a person and tell that they are bald. You can look at a person and tell that they are not bald. But you can't say exactly when they go from not bald to bald.

Since we can't know how many people are employed as developers, we must guess. But we can reasonably guess that if only 4.25% of the world's population lives in the US, it can't possibly have all the best developers, or even the majority of them.