I have an (admittedly absurd but) interesting hypothetical.
Imagine that I live in Alaska (I don't). For sake of argument, let's say I have a weekly poker game that I promote to some friends (I don't). Word gets out, and I get arrested and convicted of Promoting Gambling in the First Degree, a Class C felony (I didn't). I serve my sentence, and my parole and/or probation have expired. I am now a prohibited possessor of firearms in the United States (I'm not).
As a prohibited person, according to Haynes v. US, I can't be prosecuted for failing to register a machine gun. So, I decide--in the privacy of my own home--to manufacture a machine gun from scratch in my home machine shop (I definitely did not). I cannot legally register it, and, in fact, I am exempt from the registration requirement.
Nobody knows I have this machine gun. I go deep into the woods, and dig a hole, into which I place a safe. I put the machine gun into the safe, along with incontrovertible proof that I manufactured the machine gun at home, during such time that I was a prohibited possessor.
Ten years passes from the discharge of my parole or probation. As a matter of law in Alaska, my firearms rights are restored. I then wait 5 years until the statute of limitations expires for illegally possessing a firearm as a felon. Then, I go out to my safe in the hole in the woods, and I get out my machine gun.
What is the status of my machine gun? It was exempt from registration requirements at the time of manufacture. There is no ongoing registration requirement; registration is only done at the time of manufacture or transfer. I am now legally allowed to own firearms. I possessed a firearm illegally as a felon, but the statute of limitations has expired, so I can't be prosecuted for doing so.
I have certainly committed crimes, but are any of them prosecutable? Is my machine gun now quasi-legal? I feel like I'm missing something that makes this obviously illegal, but I can't figure out what it is.
(Of course, I'm sure that in reality I'd be arrested and my gun would be impounded, and even if I beat the charge, I'd never get the machine gun back.)