I don't think there were two versions of the KP1 rifle per se, just the trigger group. I'm not sure of the exact timeline, but the revised trigger group came along about the time Knight ceased production. It came about due to customer complaints of misfires and trigger group unlatching. I think the unlatching problem was a combination of shallow locking pin engagement and the shooters trigger finger contacting the release latch. If you compare the two trigger profiles, there's a smaller gap between it and the latch on the newer trigger so getting your trigger finger behind the latch is less likely. Some of this is conjecture because there was very little information coming directly from Knight Rifles owner EBSCO Industries/PRADCO, because they were busy shutting it down. They were, and still may be, responsible for warranty issues with the KP1 and Revolution. I've read several post on different forums of people sending problem KP1s to their Decatur AL location that was/is handling the Revolution recall repairs and getting it back with the updated trigger group. Mine has the original trigger group, but honestly I haven't used it enough to experience any problems. I hope the new KPX has some interchangeability with the KP1.
