Yes I was mostly referring to unregistered, non-restricted but now prohibited.
I suppose if you currently own previously restricted now prohibited weapons (i.e. AR-15), AND you own previous non-restricted now prohibited weapons (i.e. M14), you might definitely be one of those target for a "visit" to confirm you aren't hiding anything...
Also, just had an extremely devious idea: since the government doesn't know (other than in maybe QC) if you own any non-restricted now prohibited weapons, they can't really send you a direct email/letter as I previously opined. But, what if they send one to you anyways? As a scare tactic. You get the letter and think, "Oh shit! DO they know about the AR-10 I have stashed away in the crawl space? Oh fuck oh fuck!!" It's all bullshit and fishing, but it may get a few more people to turn in their weapons.
Also, how the hell is the M14 prohibited but the M1 non-restricted? Oh wait, never mind...