Discovery 925 SeriesVoyager ProVoyager 835Voyager 815 & 855Explorer - 220, 320, 330, 340 & 350Explorer 360 & 370Explorer 390 Pulsar 260Pulsar Headset 590/590ePulsar AdapterVoyager 510 & 510s (Headset)Voyager 520Discovery Series - 610, 640, 645, 655, 665 & 640EM2500M3000 / M3500BackBeat 903/906 HeadsetThe two digit Date Code on this headset is located on the left side, which also has the Power on/off switch. Look at the inside surface (facing your ear) and you will see a printed "CE". Above the CE are four lines of very small print and the third line has "IE XX IC:457A-BB903". The "XX" is the Date Code which is a letter and a number, for example B4 or J9.BackBeat 906 3.5mm Audio adapterThe two digit Date Code on audio adapter is located on the back of the adapter, and you will see a printed "CE". left of the CE are five lines of very small print and the fourth line has "XX XX ". The second "XX" is the Date Code which is a letter and a number, for example B4 or J9.