AP1 vs AP2 vs AP2.5 in the Tesla refers to image processing hardware and software.
https://en.wikipedia.org/wiki/Tesla_Autopilot#Hardware_1
The AP1 includes forward looking radar by Bosch, ultrasonic detectors and a forward facing Mobileye EyeQ3 camera at the rear view mirror mount. That camera does many things including rain detection. It also detects speed limit signs.
https://www.mobileye.com/uk/fleets/technology/speed-limit-in...
It's more of Tesla can't because because MobileEye owns the patent:
Tesla AP1 cars also have it, but when Tesla dropped MobileEye in favor of their own system, they can't use it anymore.
That is THE meat and potatoes of the patent. Sign recognition. i.e. speed limit signs. I'm not a patent lawyer so I will not pretend to know enough of the scope.