This has changed somewhat over the years.

In the old days, cars were mostly identified by the production year, and to make things more complicated, often marked on titles according to the year they were actually sold.

In this day and age, however, each year brings a new set of federal regulations that cars have to meet. So a vehicle is federalized under a certain year's regs. To allow for some flexibility, the date of production doesn't have to meet the regulation year. I'm not sure if they can build cars to past years or not, but they certainly can and do sometimes build cars for 'next' years regs. For example, there are already more than a few '10 model year cars out and about. US market cars are usually marked somewhere (door jamb stickers?) stating what model year regulations they meet.

To make it even slightly more murky, at least in terms of older models, Volvo used to change over the production lines for a new model year in the middle of the Swedish summer. So roughly half the cars built in a certain calendar year would be from the earlier production year, roughly half from the latter year. Volvo just gave them alphabetic names internally.

I somehow doubt I've settled any argument, other than to refer to the federalized model year, instead of the production date.
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'63 PV544 rat rod, '93 Classic #1141 245 +t