A is accurate enough to not skew the calibration results. Drifty sensors will make the calibration procedure more complicated. This makes sensor calibration difficult at best, but remember that such calibration is needed regardless of the instrument's technology - smart code still saves pots. The user inserts it in a controlled temperature bath and then enters the bath temperature into the computer. Not really, given that the thermistor requires some sort of calibration.
Every sensor does have it's unique calibration requirements.
In cases where the computer can automatically insert known readings, by all means do so. The frequent recalibration will yield a better product. If some manual intervention is needed, say by making the user subject the sensor to known values, then the self calibration techniques are still worthwhile. A little code saves several pots, and completely eliminates the tedious pot twiddling that can only be done in a lab. Sometimes, due to the expense or complexity of inserting accurate standards, a two equation calibration is not possible.