Some modifications have been made to the system today that make it a requirement that all products have unique products codes. The main reason for this change was to resolve bugs and problems in the content downloader / uploader and in related product functionality.
The only changes most merchants will notice is that when adding or modifying products the product code box will need to be filled in (if left blank the system will auto generate a code for you). It is still up to the merchant to choose if the codes are used on the website and visible to their customers (the default is to hide the codes).
Some merchants had some blank or duplicate product codes for existing products and we had to correct those automatically when we put this change live. To do this we appended a unique part to the end of the existing code in a minority of cases.