I have a 1978 CB750 that is titled as a 1979 (I'm in the process of fixing the year, it's definitely a 78 SOHC), but the frame VIN has a "K" in it. I have 6 SOHC CB750's and they all have a frame VIN that start with "CB750" and then a dash and the normal VIN number associated with the bike/year. None of them, or any I've ever had have a letter after the CB750 in the VIN. The VIN on the bike matches my title, and it doesn't look like the frame has been re-stamped or messed with. The VIN plate riveted to the opposite side of the neck also has the "K" in it, and doesn't look like it was re-stamped.
Were there bikes sold outside the USA that would have had a letter designation in the VIN?