I'd expect that a great many people would claim to have sold or moved the weapons out of state while quietly defying this law.
If there was a record of the owner’s having legally bought a now banned weapon, then the authorities could have probable cause to get a search warrant to turn over every stone on the property to find it. Out of state storage would create a whole new business opportunity for someone to open a commercial armory facility to store out of state owners’ weapons.............