If a major US ammo company markets ammo as .223Rem, it will be .223Rem SAAMI, in both brass dimension and powder charge. If you take a 5.56NATO casing and trim and resize it to .223Rem SAAMI specs, it isn't 5.56x45 NATO brass anymore, it's .223Rem.
I have LC NATO stamped American Eagle in 50gn HP. It is without a doubt, not 5.56NATO (50gn HP NATO?)
My guess (!) is that they are so busy churning out brass for 5.56mm ammo, they stopped stamping cases for .223REM production. Current American Eagle ammo also has crimped and sealed primers.
Seems to be fine .223Rem ammo, that and the AE 55gnFMJ.
Federal does make 5.56mm ammo for civ consumption (often 'factory seconds') , it is sold as and marketed as 5.56NATO though. Unfortunately the US will not allow any 5.56mm to be exported at the moment, and haven't for the last few years.