Only 7 states and DC require you to "register" your guns.
In my state (NC), I had to apply to the county sheriff for a pistol purchase permit to buy a hand gun. They did whatever background check was done. At time of purchase from an FFL (Federally Licensed Firearm Dealer) the 4473 for was filled out, and the purchase authorized with the PPP (pistol purchase permit) issued by the sheriff.
The 4473 form actually never left the store, but the store was required to keep them on file, and allow the ATF to examine them. If the dealer went out of business, then all the 4473's were surrendered to the ATF. They were never used to create a database. Once I received my CHP (concealed handgun permit) all I have to do is show the permit at time of purchase. Again, the actual information on the purchase, never leaves the FFL's store.
If I bought a gun in a private sale, all I had to do was show the seller my CHP. I did a Bill of Sale on most of these, but more of a CYA for both of us.
Now, after laws were changed in NC, to purchase a gun, handgun or long gun, it is done via the FFL calling the NICS for approval, or by showing your CHP. If NICS was called by the dealer, it in no way implies that a purchase was made. They changed their mind, their CC was declined, or whatever. Dealers calling NICS was the method used in most stated, probably still is.
So all the cop shows where they call in the SN of a gun, and immediately they tell them who the "registered owner" is, is just theater, unless it is registered in a state that requires it.