Hello all, first post! I bought Fender Precision bass for my son from a reputable store that stands behind what they sell. I am concerned there is no SN on the back of the head stock. It was sold as a Mike Dirnt. Any info would be helpful. I am tempted to take it back and ask for a refund or trade on another. I have to think it could be a knock off, yet the guitar looks excellent in all other ways. I just don't see being able to resell it someday without the SN. Thanks in advance.