Probably could be called an executive order. The reclassification of the striker and street sweeper shotguns to DD's was clearly an ATF political operation for something they had long approved and allowed thousands to be sold. Short amnesty period for the owners to register them.
Akins Accellerator had small numbers, but they had an ATF Tech branch approval letter. When they reversed themselves the owners had 90 days to turn them in or face charges for owning an illegal MG. When they banned the open bolt Tec 9 after allowing them to be sold for several years, those owners had the same treatment.
Regardless of the numbers out there, they have shown a willingness to do this over decades. They will reverse themselves/change their minds and demand compliance for something they had explicitly approved and allowed in the past. They do not give a crap about the fact you may have purchased it legally and with their approval.