A Miu Miu bag? Please help~~~ (图)

Dear all, Which one you’d better? I am thinking of the OFF WHITE one for spring & summer, but the DARK NAVY BLUE is so pretty and the leather is so shinning! As we all know, for most premium designer bags, there is a series # or product # inside of the bag for authenticity reason. Just decided to purchase a Miu Miu bag but the seller told me there is no series #, tag #, or any number inside the bag to prove the authenticity. If you have a Miu Miu bag, would you please help me to prove this is true?