Some people use the production year, and others use the first year of registration. I have a similar issue with one of my cars. Frankly, I prefer to identify my car with the year of production, as it more accurately reflects the vintage. (besides, I'm not certain of the authenticity of my car's historical "first year of registration"-- it reeks of someone trying to make an extra buck by making it look younger)
Waqas in Austin, Texas