If you look at the final bikes the factory made with a month and year code, the second letter was the season or sales year (to simplify things).
so a bike with a KG prefix was built in september 1971 but a 72 model. whereas a bike with an apparently earlier code like AG was actually Jan 1972, only the matching numbers would be higher.
The fact that model years and calendar years differed causes a lot of debate and confusion.
I have two BSA's that are technically a 71 and a 72 model respectively, but both were manufactured in 71, but have different year stamps E (71 season) and G (72 season)
