Re: "no requirement of 'registration' for deactivated firearms"
It is much the same legal "logic" that has people doing time for buying or attempting to buy icing sugar or salt from policemen who are pretending to be drug-dealers selling heroin or coke.
Or others doing time for chatting-up policemen who pretend to be pre-teen girls.
If it looks like a duck, it gets arrested for ducking.
It's not the reality that matters, sometimes, but the intent.