Plantronics CS351, CS351N, CS361 & CS361N Wireless Headset Date Codes The bottom of the base will have a white sticker starting with “B” for base. This is followed by a letter representing the Month (A=January, B=February…) and a number representing the Year (6=2006). The headset will be located under the ear cushion and follow the same letter/number combo as listed above.