The cosmic irony of your post is that proponents of a critical line will use databases as evidence that the lines are refuting. That is a big piece of how we know what the critical lines are.
This is why I said 'from the past 20 years'. Opening theory is a constantly growing foundation of knowledge. Modifications crop up frequently--new refutations are found, then refutations to the refutations are found. Both sides get improvements over time. So using recent games is a good way to control for 'what we know'. It prevents an opening with a historically high win % that was refuted later on from having unrealistically high performance in the database.
If you're saying 'well what if a refutation was found yesterday', then we don't know it's a real refutation yet. It has to be tested in real tournaments by good players to be empirically valid, and by the time its strength has been verified it will have made an effect on the statistics for the opening.
Not if, for example, a new line is found which refutes an opening and renders all those previous games useless.