When they first started doing this NICS b.s., I suddenly got 'delayed'. No criminal background, in the military, working on submarine nuclear propulsion (with a security clearance and federal background check to go with)... heck, hadn't even had a speeding ticket for a couple years.
As it was explained to me, the automated system flags that you have a background file. Doesn't matter what it is, or what it was for, but that you have a background file. Then some meatsack has to go and physically put eyes on that file to accept or decline the transaction. Meanwhile I'm sitting there waiting, fuming, 'delayed' because I at one time had a military security clearance. Joe Crackhead can go ahead and buy his TEC9 bullet hose - because he hasn't been caught by the po-po - yet - but for serving my country I get 'delayed'. As you can probably guess, that causes me no end of aggravation.
There is a simple solution, though.
Don't put down your SSN on the form.
Your race is mandatory. Your sex is mandatory. Where you were born is mandatory. Your SSN is *optional*.
They say its there to prevent misidentification that could cause you to be delayed/denied... all I know is I got 'delayed' three or four times in a row over a couple years after NICS went into effect. Then I stopped putting down my SSN, and have had nothing but clean sailing ever since.
YMMV,
Monte