Gucci does not have authenticity cards, like, for example, Chanel does. What comes enclosed with most bags are cards stating that the bag passed quality control. It does not have a serial number or even does not identify a bag model. I would not worry about not having a card, but if you are concerned about the bag's authenticity, take a few pictures and ask the helpful authenticators in the proper thread. Per TPFers, there were cases of bag switch even when bags were bought from reputable sources such as Neiman.