I'm sorry for this late reply to my question. Three weeks ago my 6 year old daughter was bitten by the neighbors dog. Once on both legs and once on the face. It has been a rough few weeks for my family. As for my motorcycle, the build date of 6/71 . After the 6th month Honda titled it as the next year. It has all the older parts that came on earlier models than the ones that came on the 1972 K2. From what i have read it is considered a 1972 K1. Then again I have been known to be wrong before.
This issue comes up periodically, and here's the poop. For the CB750, the "K" series follows the calendar years, but only loosely and only by coincidence. K1s of other models may not be anywhere near 1971. Honda itself did not use calendar years before 1974. The model year in the US was assigned by the dealer and or Bureau of Motor Vehicles where, and when, it was sold.
So you could very legitimately have a 1972 K1. But realize when talking about it you'll get raised eyebrows from those not familliar with what was going on back then. And also realize that when you buy parts, you'll need to use the serail number, denoting K1, and not the model year.
Honda got sued over this, and lost, and starting about 1975, they standardized model changes with calendar years.