Say Tesla has recorded video of some dude driving down his street in LA and their system detects a car door opening in his data stream. How can Tesla find out whether or not there actually was a car door opening? Human labelers (for billions of miles of data)? Multiple instruments?
If I were designing a system, I'd want a car with extra instruments on it that would help me validate what the primary instruments detected. The idea of just recording a bunch of live traffic seems pretty lame. (You have no way to validate any of the conclusions you draw from the data and hence no way to improve your ability to draw conclusions from the data.)
Did you see the article about Waymos test environment at Castle? That, along with a boatload of simulation, is exactly the kind of testing you need to do to develop this kind of a system.
Has Tesla ever demo'ed their simulation environment or other tests?