Dating a bicycle -- or determining the model year a bicycle was manufactured -- is seldom an easy task. Few bicycle manufacturers keep an easily accessible database of previous model years before the year 2000, and a company continuing the same frame style over multiple model years usually taints serial number records. There are some tricks to dating a Specialized Hardrock though.
Go to Specialized's website and peruse the online archive that catalogues Specialized bicycles built after 2002. Proceed if the Hardrock in question is not listed.
Click on "Contact Us" and record Specialized's number.
Flip the bicycle over and write down all number and/or letter groups pressed in the bottom of the bottom bracket shell -- the metal shell housing the crank spindle and bearings -- of the frame.
Call Specialized and ask to speak with the warranty department. Give the serial number and ask for the year of the bike. Proceed if serial number is unlisted.
Call a local Specialized bicycle dealer and ask if it keeps a library of bicycle model year catalogues that you may look at. Many shops keep these industry standardised catalogues for just such an occasion as dating bicycles. Proceed if this produces no results.
Ask to speak with the most senior mechanic at the Specialized dealer. The odds are good he can pinpoint it within three years based on components and graphics.
If all else fails, post a picture on online bicycle forums and chat rooms. Someone may see it and be able to help. Bicycle shops that are not Specialized dealers may still provide some of the knowledge needed to pinpoint a date if no Specialized dealers are available in the area.