Sorry, the NFA was ratified in 1934 as a result of the ST Valentines Day massacre, the NFA defined title two firearms: machine guns, SBR, SBS, AOW, suppressors and destructive devices. The spirit of the SBS and SBR regulation was to prevent 'the mob' being able to conceal a rifle or shotgun without the gun and owner being registered with the approval of their local sheriff. It also defined title one firearms and non firearms, black powder, smooth bore canons, etc... The 1968 GCA was ratified to allow for amnesty of unregistered title two firearms, war bring backs and such. The 86 GCA defined pre and post samples and 'froze' the machine gun registry no longer allowing new form ones to be submitted..It means that current and future prosecutions that rely on rules that were established as a result of Chevron deference MAY BE challenged in a court of law.
None of those rules will be struck down until someone challenges them in court and the challenge wins.
In this particular situation, this doesn't apply. The relevant law here is the GCA which was passed - including the definition of 'rifle' in 1968.

