The problem with identifying your bike by 'year' is, that it will not help you looking up things in
genuine Honda documents.
Best starting point is: compare the frame- and enginenumber of your CB500 or CB550 to those listed in the first four pages in the various CB500 and CB550 parts lists. I don't understand what's against that? After all,
you only have to do it once. These parts lists were meant as reference for dealers! When you consult the paper editions, carefully collected and published by volunteers, you will be also informed on modifications
during the term of your model and will have a perfect overview, like in this one:
https://www.honda4fun.com/dwnload/Part-List/CB550/CB550-K0-K1-K2-Parts-List.pdf The CB550(K0), K1 and K2 on
one page. What more could you want?! Talking 'years' will confuse many and could also confuse
you. We have ample proof of it in this here site. Realise also that this happens to be an international site and that nowadays various models surface just about anywhere. This 'year' thing has even confused an in general pretty trustworthy site like CMSNL. On the page where they list 31 CB550 models, the first one listed already leads to confusion:
CB550 FOUR 1975 CB550K0 USA it says.
1975? A
K0? Really?
Europeans don't understand why the year is sooo important to Americans. For us a bike is a means of transportation, not some fashion article. The CB500K1 has been marketed in the UK for I don't know how many consecutive years. The same for the CB750K2 in
all of Europe. It has been years before its successor arrived: the CB750K6; the K3, K4 and K5 have not been imported here. If you want fo find out about your bike and also want to detect possible bastardisation, the best strategy is to learn what your model was in
Honda speak when it left the assembly line to be shipped.
My bike was first registered in 1977, imported in 1976 and assembled in 1975.
Who cares?! I have a painstakely edited parts list at my disposal that perfectly informs me, also on modifiations during its term and as, a bonus, shows the differences other destinations had and so offers me a variety in parts to choose from, to my personal taste. Thank you Honda!
To end this in good humour: years ago a German guy witnessed in disbelief a heated debate in some car forum about what 'year' a certain Ford Mustang was and was not. To calm things down, his down to earth reply had been something like: "Guys, what's the fuzz? After all you're only looking at a yester years Falcon!"