Good question. The ATF/DOJ have been data mining at local law enforcement for several years now; looking for the gray areas in old records, etc. Many people are finding they are suddenly identified as a Prohibited Person and denied to purchase even though they have never had a problem owning and purchasing firearms from FFLs for decades.
DOJ asserts you are a Prohibited Person and your rights are denied without due process. Even though they have access to the same old court records and medical records, etc., as you, the burden of proof is on you to clear your name.
Meanwhile, during this time you technically a criminal unless you have your firearms secured where you can not have access or control. You may choose to keep them with you, but you will be in constant fear because you do not know if you will be one to get a late night visit from the storm troopers. They have your name. They know you are now labeled a Prohibited Person. And they know where you live. You never know if you might be the one to get a visit.
It can easily take a a year or more and serious money as it is best to hire an attorney. It usually takes at least 4 to 5 months just to find out why you were denied.
Its not just old court records. They are also data mining old medical records for such things as visiting an MD or admitting yourself to a hospital for depression during a difficult time, such as an old divorce, loss of a loved one, PSTD, etc.
Some have had to sue in Federal court to prove their rights are being violated. That's when the big dollars kick in.
Google it. This has been going on for the last 4 or 5 years. Just wait till the get the national registration/er background check is installed. The Prohibited Person list is going to get real big.
Anyone who has had a DUI, who was recommended for 'treatment' (almost a given in some jurisdictions) may be a target.
Anyone who ever got busted for dope back in college, (even if that was their 'come to Jesus moment' and they never smoked it again)...
Hard to say with so many laws and such moving thresholds for offending anyone, just what will be made into a disqualifier.
There are days when I think a really good EMP would be a blessing. Back when, people could grow up, move, start over, and now every infraction follows them wherever they go (short of joining and serving a hitch in the French Foreign Legion).