The model years put on titles back before 1970 or so tended to be pretty casually related to the production year. Since 1970 (or near) each car built had to meet that year's thick stack of federal regulations, so the production date became very important (and subject to some odd wrangling occasionally). But prior to that it just didn't matter, and it was usually just the calendar year in which the car was titled. So your car may have been built in 66, but sat on a dealer's lot until '67.

To confuse things farther, Volvo's production years used to change over in the summer.
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