To answer your question directly - no, I don't have the documentation.

But don't wheel speed sensors detect the rotational speed of the wheel, not the forward speed of the car? Such that the diagnostics screen would have to calculate the speed displayed (and perhaps introduce the same error that the speedo has) rather than just pass on the raw value from the sensor?

I understand the value in the diagnostics screen to be the lateral velocity as calculated from GPS triangulation and not via the wheel speed sensor.

One way to prove it would be to disable the GPS receiver (by either driving underground or just unhooking it?)