If its a Datsun its an '08. If it says Nissan its an '09. JK of course..
Yup - there is no such thing as a 2008 Nissan 370Z. The 2009 is the first model year so while yours was build in '08 its still a 2009 Nissan 370Z. Every manufacture is different as to when the manufacture date and the model year ends up....
Oh and "Go Datsun"!