You are probably correct and for me, it was just wistful thinking but I figured I read it somewhere that a change of one would eventually self calibrate.I think you still need to recalibrate after changing a single height sensor.....
I cannot find that article however but I did find below from an LR3 suspension overview which agrees with your comment. This means the GAP tool or similar such as my Black Box is required.
Calibration
A calibration routine is performed using T4 to read the position of each corner of the vehicle and record the settings in the ECU memory. Once set, the calibration is not required to be performed unless the air suspension control module is removed or replaced, a height sensor is removed or replaced or a suspension arm to which the sensor is connected is removed or replaced. If the removed height sensor is subsequently refitted, the calibration procedure will have to be performed to ensure the integrity of the system.
If a replacement drop link is fitted, recalibration is not required providing the sensor body is not removed from its mounting bracket.