The year is irrelevant. My bike was first registered february 1977, meaning it has then been handed over by the dealer to the 1st owner that took it to the street. Who knows how long it had been at the dealers or when it was imported? When it was built? Who knows? The parts may have been assembled years and years apart. I don't rule out mine was in a batch of leftover engines, that to empty the shelf it occupied, was given various parts you find on the CB5
50K2. All I know, after comparing my engine- and framenumbers with those listed in the first few pages of the CB500 Parts Lists, is, mine is a CB500K2-ED and that's all what matters. I'm a happy man know. Not before, when e-ve-ry manual I got my hands on, was frustratingly incorrect. That period lasted over 25 years and only this year 2019! I've managed to find the appropiate wiring diagram for my model. BTW, this is the kind of info, you will not find in the fiches, as displayed by CMSNL. Neither do you find info there concerning colour codes, carb numbers, etc. Just leave the 'year' to advertisers:
LOOK! Our 1975 model now features bigger indicators and a bigger taillight!!! Isn't that great?! Hey, isn't that what you always wanted? Bigger? The 1975 Honda, now bigger than ever before. I'm lovin' it! For sound info go here:
http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb500 and
http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb550 It's the first thing you should do when you acquire a CB500/550.
Stop talking years. It doesn't mean a thing, does not refer to reality and much too often leads to confusion.