I wonder if pookie is misremembering things. During the ban it was illegal to have a flash suppressor, or a barrel threaded to accept a flash suppressor. The BATF determined that a muzzle nut was not a flash suppressor, because it did not FUNCTION as one. The BATF also determined that it was legal to have a rifle with a threaded barrel so long as you had the muzzle nut (which covered the threads) as long as the muzzle nut was permanently attached (as the BATF defined that).
The question of legality during the ban is different than 922 (r) compliance. The list developed by the BATFE regarding countable parts does not refer to the FUNCTION of the "muzzle attachment". The FUNCTION was crucial to the question of whether a muzzle nut was legal during the ban, but irrelevant now.
The BATFE has not made a determinaton that a bayonet is a muzzle attachment, but now that you've put the idea in their heads, expect that to change if there's an Obama bin Biden administration.