Jason, what you say makes sense, but we are dealing with governments!! Since when do they care about making sense??
Since Norton only had frame numbers on Commandos in 1975, the engine number was always stamped into the frame tag. This is what was used as a VIN for all pre-75 models. It is really up to the motor vehicle department of the original licensing state (and to some extent the dealer supplying the VIN and Bill of Sale) what number is used to title. All the Mk III titles I have had or seen (Mich, Ohio, PA, KY) did not use the frame number as a VIN.