Not sure this can be answered for the general case, but is there any way to 'predict' or recognise what kind of changes there may be between the various generations (if that's what we should call them) of robot models? Or in other words: what makes Fanuc decide that a robot should be an iA/iB/iC/iX?
The LR Mate is the clearest example where even their physical appearance changed going from iB to iC to iD (curiously there appears to be no 'iA', probably to not confuse them with the larger robots?), but for other models such as the R-2000 iA and iB (or the M-710iA/iB/iC) it's not really clear where the (biggest) changes have been made.