Hello, Nancy and thank you for using our new support tool. Your question is a good one and is based on standards established by GS1 and used around the world. For my answer, I am assuming you are asking only about the UPC 12 barcode. Let me know if I am wrong as I do not want to steer you the wrong way here.
In the non-GDSN world, your consumer products must have a 12 or 13 digit barcode in order to be scannable at the point of sale in the U.S. So, for your UPC, it is likely a 12 digit number based on your company prefix. To represent that number in GDSN, yes, you would add two zeroes to the beginning of the prefix to create a 14 digit GTIN for GDSN product communication.
The last digit in your UPC is called the GS1 Check Digit and is an algorithm of all the numbers that preceded it. By adding two zeroes to the beginning, it does not change anything mathematically. This is why, when you use your UPC to create non-consumer units by adding a 10 or 20, etc, you must also get a new check digit as it changes the algorithm.
I hope this helps. Please let us know if you have any other questions.
