Also, Uber outright refused to comply with California law and register their self-driving car program, and it's looking more and more like the reason they did that is so they didn't have to publicly disclose those disengagement numbers.

I suspect you're right. However, a higher number of disengagements could just point to a more cautious approach, more difficult environment, etc. Hard to pin it exactly to maturity.

For example, I believe Waymo cars drive mostly on a fixed number of preplanned routes. You would expect limited disengagements over time, as it's got tons of data on those specific routes.