I talked to GAP about this. Looks like it only works on 2015 and 2016. Not all of the 2014s have the harness and supposedly the code for the adaptive cruise isn't in the ECU. Sounds weird to me, since the ECU has the same part number as the later ones, but they're the experts. They also said you can't put a 2015+ ecu in a 2014 car without changing other modules, and you can't flash 2015+ software to a 2014 ecu.
Interestingly I saw this LR4 for sale in town with the ACC option. although they don’t have it listed as a feature, you can see the controls for it. First one I’ve seen with it actually. Did it come on all Lux vehicles or was it still an add on feature?