To me as a Systems Engineer, and systems modeler, I thnk you've slightly misquoted an old saying "Garbage in, garbage out".

It the case of any control system, it isn't true. We start with an initial value which will most likely be random garbage, and the controller homes in on the value we need out of it. This is the whole point of the controller.

I don't see Ai being much different, by being a learning system, it can start with garbage in, random or otherwise, and end with coherence and truth, given it has enough "Sensor" inputs, and the ability to overwrite the initial data. I guess it will have to have this ability to qualify as a system capable of learning. In the case of Ai, the sensor inputs are us interacting with it, millions if not billions of us. By that it can quickly gain the wisdom of the crowd, which is often different from even the most expert individual in the crowd, but usually closest to the truth.