There has been engine updates since day one. Every engine we get into we see differences. (Bearings, balance shafts, clutch hubs, etc... ) 2014 was a year for new clutch hub and front fender and stopping of gold line brakes. Everything is interchangeable tho. New stuff has tighter tolerances. 2016 From what I know, the ECU was the largest change in mkII and to "mark" this they also changed seat style. The new ECU does seem to make a better running bike. But not without sensor, coil issues. MY OPINION ONLY>>> Any and all norton 961's NEED a total sensor and ignition upgrade and someone to check every bolt is tight. Ran in properly from new. After this, you will be rewarded with a really fantastic motorcycle.