AI's goal with patenting the KeyMod system was to standardize it. As Tom stated, the design belongs to AI. SA or LA, the KeyMod dimensions and such are the same. The AX/AXMC share the same attachment methods.
I know what you guys are talking about here though - mainly the fact that the KeyMod system isn't retroactively listed as a feature on the AX rifles AFTER the 2014 release of the AT/AXMC. Probably has something to do with patents from a certain date forward.