FWIW, back in the late '90s/early '00s, when NFA Branch was still in a basement in D.C., the volume of forms was so low that they reached an examiners desk within days of arrival there (but it still took six months on average for approval).

There were no customer service reps; instead, each examiner took a turn answering the phones on one day. They were also trying to do their work at the same time, and they got a lot of angry calls, and they were known to get so PO'd at a caller that they would find his form and move it to the bottom of the pile.

I quickly learned to be very polite, very sympathetic, very friendly, and never had a form "buried." In fact, more than once, the phone-call-answering examiner said, "Oh, yeah, I've got your form right here. You've been cleared by FBI, I'll sign it right now."

Since I always had at least two or three Form 4's in the works at any given moment, I'd always follow up by saying, "By the way, I have some other forms pending; if you sign them, too, it will clear out a few more." And more often than not, they would walk around the office, collect all of my forms, and sign them all.