I am merely suggesting that a correctly followed speed limit would not distinguish map reading from sign reading. It could be either. If, as I experience regularly, the sign says 65 mph, and the car goes 45mph, and the software on the screen displays 45mph, it isn't reading the signs. It might also have no map data, but defaults to the correct speed. It still isn't reading.
What test has been done to prove that the car reads and follows the sign it reads? Has someone stolen a legitimate sign and planted it somewhere to see if their car follows it and not the proper speed for that section of road?