As you are probably aware at this point Google Shopping/Merchant Centre is going to start enforcing GTIN/EAN/UPC numbers from 16th of May 2016. If you are not sure what does it mean we hope you will find some answers below.
So GTIN is a fancy name for an umbrella like concept accommodating and normalising various Universal Number notations such as ISBN (Books), UPC (USA version of a barcode), EAN (European Version of a barcode) and more...
Basically, GTIN is a 14 digits number, it can be an EAN number with pre-appended 0 so it becomes 14 digits long, or it can be a UPC number with two...