I would assume that Google Maps vans aren't driven in the same manner as other cars. They've got a large complicated camera system on top, so presumably they're driven very conservatively, and presumably they're also not driven particularly fast (kind of hard to capture good pictures when you're driving really fast).
Which is to say, if Google wants self-driving Google Maps vans, then collecting data using Google Maps vans makes sense. But if they want general-purpose self-driving cars, then collecting data using Google Maps vans will only give them a very narrow set of data.
Again, speaking as someone who has knowledge of the products, I can tell you that the Google Maps vans are useful for recording geography but would not be terribly portable to a new sensor suite mounted to a different car.
In the OP where I mention outfitting an example 2019 car, that car might be a current-model-year car with roughly similar vehicle dynamics to the proposed 2019 model. The only thing that they are paying particular attention to is the specific sensors in use and their placement on the vehicle. This apparently is critical to development of the driving model, the camera on the test vehicle must be in the precise position and direction and must react in the same way as the production model or the data is bordering on useless.
Now, with a full 3D pointcloud and enough sensor data you might be able to translate one recording into a lower-resolution resampling to model the production version, but I've not heard of anyone doing that. Test data is collected on the production sensor suite, no changes allowed.
But Google Maps vans cover land comprehensively, whereas Tesla's "convenience sample" is not comprehensive. However, Tesla's data then covers the relevant data more often.
Definitely two data sets that should be put together.
But they intentionally don't cover the same ground frequently, which is a key part of the Tesla data. The same intersection in many different conditions is pretty important.
I'm assuming that once a Google Maps van has covered an area, it intentionally avoids that area until a significant time later.
