I currently have 12 NFA items in my inventory.
Over the last 10 years, or so, I have not been asked to show papers once.
But, you are not LEGALLY required to provide that paperwork to anyone but an ATF agent.
That being said, discretion is the better part of valor if confronted by someone not legally authorized to see proof of a stamp.
I carry digital copies of all my stamps on my phone with originals in my safe at home.
Over the last 10 years, or so, I have not been asked to show papers once.
But, you are not LEGALLY required to provide that paperwork to anyone but an ATF agent.
That being said, discretion is the better part of valor if confronted by someone not legally authorized to see proof of a stamp.
I carry digital copies of all my stamps on my phone with originals in my safe at home.