The date code of the DuoPro family of headsets will be located under the ear cushion.  The first two numbers represent the month (01=January, 02=February…).  The two numbers following the dash represent the year (04=2004).  Next is the model of the headset.  An “H7″ represents the DuoPro.  If an “N” is present, the headset is a noise-canceling model.  If an “R” is present, the headset has been re-manufactured or replaced by Plantronics.  Any trailing characters are used by Plantronics for coding purposes.