How stupid are you?
First, “they” don’t know where half of them are.
There are boat loads not “registered” or required to be “registered”.
Signing background check paperwork IS NOT “registration”.
Private sales, family gifts, theft, and loss, are NOT reportable transactions.
I think that is where they will actually start.
There are many “off the books” firearms out there.
But to remain outside “their” spectrum of interest, these firearms holders must not have any other indication of ownership.
No evidence (credit card, mail order, video surveillance, neighbor’s reports, etc.) of ammo purchases, accessories, targets, visits to ranges or shooting areas, related magazine subscriptions, etc.
The owner can’t also have any “legal” firearms. That puts him under the microscope.
Maybe the theory is give up the ‘registered’ ones when they ask, but retain the others. Don’t know how well that will work out. Being an owner makes him marked, forever in my opinion