I'm going to take a wild guess, but when I hear 'calibration' I think 'wheel ticks'. meaning, dead reckoning.
has tesla ever had that or advertised/bragged about it? its a feature on some gps chipsets and its quite complex, to say the least (to design for and implement).
in short, it helps extrapolate when you lose gps, signal-wise. using the steering angle, wheel tick counter (revolution counter) and some other things (gyros) you can fill in missing data when gps 'goes away'. and it does go away, all the time (but we never see it directly, since software does not report it to the user unless its gone for a long time).
I've heard Karpathy several times in his presentations mention wheel-ticks, steering angle, etc, as some of the inputs they are working with for AP, so it appears the answer is yes.
The uBlox Neo-M8L-05B DGPS unit used by Tesla is capable of CEP =1.5m in horizontal and =3m in vertical plane with SBAS (a geostationary satellite signal supplying error-correction data from calibrated ground stations), but the latter only updates at 1Hz, so the IMU is used to work out the position at 30Hz in between refreshes, or when in a tunnel, etc, reputedly giving a CEP accuracy down to 2cm!
(not quite sure I believe that last figure myself)