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The manufacture date can be worked out from the first 4 numerical digits of the serial number.

The serial number is normally a 13-character code that begins with an "S". This is located on a White sticker with a barcode, and in most cases will be located on the bottom of the device or near the power input on the rear. 

For example:

The first 2 digits following the S will indicate the year, 18 = 2018. The next 2 digits would be the month of manufacture, 09 = September.