The AWB was a ban in name only. Everything in private hands prior to the ban went into effect could be kept or sold, no problems. The AWB banned new sale and importation of 19 models by name and anything with two of six features (if I remember correctly) such as a bayonet lug, threaded barrel, pistol grip, detachable magazine and so on. The AR-15 and M-1as were still readily available after the ban because the manufacturers sold them without the "evil" features.
Everything was grandfathered in NFA registered or not. If you register an SBR, it does not matter if it is assembled or not, it is still a short barreled rifle.
Between 1994 and 2004 you could see kits or guns labeled as pre-ban and post-ban. The only difference on the AR-15 parts was whether or not it had a threaded barrel or a flash suppressor.
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