Thanks all. This is my understanding based on Cobra Transmissions page ... the NV125 is the model and the LWC/X and ATC are submodels. (see
BMW X5 Transfer Case Parts : , Cobra Transmission).
In my case I have NV125 manufactured on 9/11/2002 with the cars build date just after. So I believe I have the "one blue link" chain which I equate to LWC/X 500 and not the 2 blue link chain associated with ATC.
Hopefully I will get to the chain replacement soon and know for sure.