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I see examples go 1969 models that had a 17000 VIN number on the engine and had a manufacture date of 12/69 and was registered as a 1969. I assume then that no 1970 models were manufactured in 1969. I believe the 1969 model years started production in 6/69. Answer or correct me as you will.
Back in that period, most states titled motorcycles in the year they were sold. Example: If a Sandcast was a demo and sold in 1970, it was probably titled as a 1970 model. If an early K0, post Sandcast - pre K1, was sold in 1969, it was probably titled as a 1969. It was a few years later when the government or DOT made motorcycle manufacturers supply bikes as a specific year model. Honda supplies a "Manufacturers Statement of Origin" to their dealers that has both the frame and engine numbers on it that when registered to a buyer, becomes a state title. Most states, but not all, titled bikes by the frame number or frame and engine number. Wisconsin for example, titled bikes by their engine number until the government enforced specific year model bikes.
Early Sandcasts did not have the manufacturing date on the label/tag on the right side of the neck. Later Sandcasts did. Not sure what year Honda began putting the "Year Model" on the tag but I have a K5 that does not state the year model on the tag - just the manufacturing date. I have a K6 that has the manufacturing date and shows to be a 1976 Model on the tag. So I speculate it was 1976 when motorcycle manufacturers were forced to include the Year Model on their MSO's.
This list below is not 100% accurate as stated previously but the general year/model for CB750's was:
1969 Sandcast (some K0's sold in 1969)
1970 K0 (some Sandcasts sold in 1970)
1971 K1
1972 K2
etc...