Calibration occurs naturally, only after driving the distance of say 1500 miles (may be less) the car will have enough data to gather a sense of it's surroundings and become more confident in it's ability to judge positioning, but as always, you are the driver, you are responsible, treat both TACC and Enhanced Steering Control (I don't use the word autopilot anymore) as a 12-14 year old child with zero experience on any road, and learn yourself when to take control in situations you feel the vehicle is not up to handling well. Each interrupted Enhanced steering event is logged and data recorded and gathered, so that the fleet can learn from the corrections made and eventually share that info with all the Tesla's in later firmware updates.
I don't think this is correct. Tesla claimed there was some sort of calibration needed when the parallel parking feature came out and I guess that was true but I never heard nor experienced that with the other functions of AP. People should be careful with their speculation because new people might think it's true.