Most of us know when our cars were built, so why don't we celebrate their birthdays?

It's my birthday today and I was born the same year of my racecar, a 1968 Barracuda. Technically though, my Barracuda was built in 1967, so it's older than I am. I'm not sure why car manufacturers are allowed to call a car built in 1967 a 1968 car. Maybe people should be the same way. A person born in 1968 is actually a 1969 person. Then I'd be turning 39 instead of 40 and my resale value would be higher.