During the AWB, you could SBR anything you wanted, but the NFA did NOT supercede the AWB. Your Post-Ban semi-auto that was SBR'd could NOT have 2 or more of the restricted features. Furthermore, attaching an NFA suppressor to your semi-auto counted as a flash hider, so if your firearm was a Post-Ban and already had 1 restricted feature (like a pistol grip), then attaching your suppressor counted as restricted feature #2 and created a new AW in violation.
Your Pre-Ban semi-autos were Form 1able without restriction during the AWB, exactly like today.
The AWB did not apply to MGs or any manually-operated NFA rifles or shotguns. Suppressors were, in themselves, not effected by the AWB, but the firearm to which they were attached was.
922r does not apply to NFA firearms and this is what confuses people sometimes. The AWB and 922r were not the same legislation, though they are commonly mistaken for each other.