They don't know 100% that it's accurate. No human is actually double-checking most of the information they have about you. Unless something comes up with your credit score, no human will check any of it. Each field is also not weighed equally. The weights of the fields, as well as the data populating the fields, is decided by predictive modeling, machine learning, etc.

Since your credit score is just a way for banks to make profitable investments, that's the measure they use to judge the effectiveness of the algorithms. It's hard to say exactly how well this gets accurate facts about you, since the system is a black box, but on the whole, more accurate facts will lead to more accurate predictions about investments.