Andrew R Stewart 

Some companies have a date code within their serial numbers, some don't and instead have a factory and production run code. Since a brand might have used three or more different factories (especially a brand like Diamondback which isn't a manufacturer) during any one year producing it's line up tracking for recall reasons is more important then for model year. Most modern bikes are dated by the specs, usually found by old sales info. Color, parts specs, frame construction styles all are strong indicators when compared with a brochure or photos. Andy.