Your flash suppressor is most likely not USGI. SAI quit using USGI parts, intermittently because of supply issues. I still have some real USGI parts on my '08 Socom though fromthe factory.
SAI quit putting a bayonet lug on theirs I'm certain to expedite shipping to every state but CA, here we have the CA approved muzzle brake. Also, it's speculated that they did it to make money from people buying aftermarket flash suppressors w/lug to make extra money, they are but I think it's secondary to quick supply line movement, and that means parts that will pass the most amount of states.