Perdomo Sort and Final Markings?

I didn't see this asked before but is there a significance to the Perdomo stickers on every box, that have sort and final on them, other than letting the manufacturer know who sorted and did the final inspection? Or are they some kind of grading on how good the box is? I had always thought it was just to show who sorted and did the final check but today I received a couple of boxes in the mail and one had the letter B for the final and the other had the number 12.