Can anyone here who works at Sephora (or anyone really) please explain to me why a Sephora store would keep lost beauty insider cards that people turn in?

So here's the story: As soon as I upgraded from a beauty insider to a VIB I noticed my purchases were no longer showing up in my purchase history and my point balance was not matching the cashiers screen vs when I was logging into my account. The cashiers screen was showing up that I had less than when I was logging into my account on my own. So I called Sephora customer service and it turned out I was actually given someone else's card. I asked how that was allowed and the lady said that when someone finds someone's lost card and brings it to Sephora the employees won't just throw them away they'll just keep them as new cards. Anyways, the lady said to ask for a new card next time I was in Sephora and that should straighten everything out. Well I got a new card today and my point balance is not what it should be. Now next time I go to Sephora I have to ask them to give me a blank card and have them call Sephora customer service. I know I have a solution but this is just very frustrating especially because I so could have gotten the NARS 500 point set today but alas I could not because my points weren't correct on their system. :( So my question remains why would they keep people's lost cards if they know this kind of thing can happen? I can understand that the person who lost their card could come and see if anyone had turned it in but still. I'm sorry this is so long!