The manufacture date and the model year may indeed be different. It is typical of all manufacturers to build new models in the prior calendar year. And this makes a lot of sense; otherwise, come January of any year, they would have no current models to sell for a long time.
With more modern cars, including Alfas, it is pretty consistent for the first editions of the new model to have a prior year manufacture date. The manufacture date is usually somewhere in the second half of the year that it is being manufactured, and most typically in the last quarter.
I don't know if this car is a 1967 or 1968 edition, but it should not be difficult to figure out because of the uniqueness of the 1968 model year. (Which may also tie right into why it may be more difficult to get a 1968 model through inspection.) There were no Alfa Romeos imported into the USA in 1968. New regulations took effect on that year, and Alfa's strategy to meet the new regs involved using the SPICA fuel management system, which Alfa knew would not be ready in that year. Hence, Alfa announced ahead of time that they would not be importing any cars into the US in 1968, and the first roundtails with SPICA injection (and 1750 engines) came in February of 1969.
For those reasons, if this car was originally sold to the US, then it would be a 1967 model. If not, then it could be a 1967 or 1968. There were 1968 editions imported into Canada, and brought to the US in 1968. (That was legal back then.) Alfa does keep records of where the cars where sold to... (It just takes an email to [email protected]