Kenko USA may also have a unique number. BTW, Adorama confused a lot of people when the DGX came out because they did not update the SKU or description until Helen Oster read about it on a forum and had it corrected.
I'm sure that minor production changes happen all the time, but a firmware change should be indicated somehow. Having worked in a large manufacturing company, electronic parts and processes are constantly being updated due to new vendors, new equipment, newer materials, and so on. The rule of thumb is issue a new part number if anything functional changes, but its a fine line if a better plastic or a different process is used that should not affect the product. It cost a bundle to change a part number, so you try to avoid it.