I was in the US air force for 20 years, now retired (in theory only), That entitled me to be stationed in many states where I had to title and register vehicles. So I have significant experience in the variety and differences of vehicle paperwork.
In England there is likely a single "national" policy.
Here in the US there are 50 different jurisdictions. Some strict and unyeilding policies that fly in the face of common sense and others that are wishy washy and almost anything goes as long as you cough up the $$$$$$.
Now having been in the BSA, Lotus and Norton clubs for many decades I have continued to be amazed at the complete ignorance of registry clerks and the variety of legal compliance.
So ultimately government assigned MY should be of little concern as it has little meaning as I have repeatedly discovered. What "should" happen and what "does" happen in paperwork processing can be quite different and I think you are naive to not acknowledge that. The older the vehicle is, the more discrepancy I would expect to find.
On occasion our club provides assistance to correct MY if the jurisdiction allows it.
If you expect to have me declare a unified policy in this country you are delusional. It may be more consistent now a days, but it is still not rational what some jurisdictions do....
I know what happened to my 70 paperwork. I repeat I sold it in 72 and don't have the memory to recall the date of mfg on the VIN plate or if I ever bothered to look at it. Simple, new bike, certificate of origin
.....first registered as a new bike in the fall of 70 when every day the clerk is titling and registering vehicles as 1971 so the clerk puts 1971. In 1971 what the hell do I know about shiny yellow nortons if it's a 70 or 71, so who am I to argue. 20 years later I now know better, since I still have a pix of the bike.
Major vehicle manufacturers like GM model may have a MY policy but we now know the MY for norton is rather meaningless and the MKI, MKII, MKIII designation etc is more useful, though I am not fond of it and to me seems a bit more history revisionist.
In my opinion there is no such thing as 76 and 77 commando, only "late release" 75 MKIII. I am not aware of a separate 76 or 77 shop manual
or parts book, but I'm not stupid enough to try and sell my view on this matter.
Sorry I know of no MY regulation at the federal or 50 state level and I especially doubt that a Dec 1971 British specialty vehicle manufacturers would comply to the letter of the law.
IIRC 200205 and 202206 were all made in dec?
2000 units? in one month?
I do think you are missing the wishy washy point....MY is not as clearly defined as might be desired to allow nice tidy MY definitions to allow the inclusion of combats as 73 MY.