If the thing gets reclassified as prohib, (which often seems to follow a pulled FRT number) the prohibition will apply to both restricted and non-restricted versions.
I suppose the biggest difference is that if a registered restricted gets reclassified, the owner will be notified, and given legal options for disposal. In the case of a non-registered non-restricted, there cannot be any notification, so if the owner gets tagged with it, it will go directly to prosecution for possession of a prohibited firearm. Anyone who makes or transfers one would also be subject to prosecution.