"no requirement of 'registration' for deactivated firearms"
Right, so people are automatically going to volunteer the information that they had a deactivated firearm. Sure. That will in no way bring attention to them, there will be absolutely no investigation launched into people who "notify" several weapon transfers, and nothing bad will ever come to the people involved.
Come on, you don't require registration of such weapons, why do you suddenly need notification of change of ownership ? That is equivalent to saying that someone else now has it, which is the same as a registration in that person's name.
Might as well impose ID cards.