I don't think that determines it's authenticity, I have an MK Jet Set that I got maybe 5 years ago that has a piece of leather behind the charm and it was purchased at the MK Flagship here in Toronto. I'm sure there are other bags as well that have it such as the Sutton or the Jules crossbody. If you're uncertain about a bag's authenticity try reaching out to a company that provides authentication services or post the bag in the MK Authentication Thread but ensure you meet the requirements and follow the appropriate guidelines.