I would call your closest Sram Distributor/dealer. Sram is hard to call without the right number to direct dial someone. They will be able to point you in the right direction of authentication and what your Serial number means.
I'll say right off the bat, the way the steerer and SN look, it looks genuine. Counterfeits seems to mess up the crown details as well, and yours looks nice and clean. Finally, that paint on Rockshox forks is not easy to replicate. What I'm seeing in paint also looks accurate.
I'm only looking at one picture on the internet though, and I could easily be wrong about it all. In your position I would definitely call a Sram dealer and see if they can connect you with the right person.