I got delayed one time about 12-15 years ago. Found out someone with my same name in California had a warrant out for their arrest for bouncing checks. I finally got approved 3 days later. Didn't know why I got delayed at the time, however about 2-3 months later I went in to get my drivers license renewed. Lady called a deputy in, and he stood their with his hand on his gun. She asked me if I have ever been to California, I said no, since I haven't. I showed her my picture CC permit. Anyway, she then said someone in California with my name had the warrant out. The deputy left, and she proceeded with my license.
Getting delayed can be a simple matter of someone with your name having a warrant out, a restraint order, or a felony conviction in another state. Giving them your social security number when you get a license helps them to look it up quicker.
Anyway I haven't bought a new gun in years. Got all I need to do all my hunting and self protection needs as well as clay shooting and target practice.