The reference I saw indicated it was for FN carrier (rarely ID'ed part), charging handle (also rarely stamped), upper (the forging die used was made for FN, hence the mark but machining???), grips (again, FN doesn't make them...)and FN stock. All but the stock I know are NOT marked. Just barrels, sight bridge, hammer and a few others. For the most part, this is an ad gimmick. Avoid like the plague.
Not all FN "rejects" are junk. I got a few servicable parts from a dealer, namely an A2 hammer with deformed auto sear hooks (unservicable for the most part but since AR's don't need them...)and a barrel that was too tight on headspace (barely chambered factory ammo). The barrel has loosened up considerably but its still stiff with factory ammo.
DPMS is the likely vendor for many of the small parts. They have some standing contracts for rifle parts. Matter of fact I have in my pocket one of their firing pins but I dare not say its an FN. Why? Small collar, so its an AR part.