Well I can only go off of what the factory Nosler rep told me when he was in my store in person (I'm no longer there btw). Norma makes all their brass, with their (Nosler) headstamp on it. Some of the cartridges they have an exclusive deal with Norma on, so you won't see it offered by Norma themselves, nor will Norma supply it to anyone else (supposedly) in the future.

And I also have a 257 Roberts AI. I would hope you're not losing any brass when FF'ming AI brass. That's kind of the whole idea behind the true AI chambering. I have also fired factory ammo from Rem, Fed, and Hornady out of mine, and it FF'd perfectly fine.