"And out of those 13 million only 47 bought guns, legally."
The media are horrible at explaining just about any kind of research study. They're not only generally ignorant of a wide range of subjects, they're also so certain that a journalism degree allows you to explain ANYTHING, that they don't bother letting somebody who DOES understand what they're reporting on look at the copy before it's published.
I would guess that what they really did was to cross check incoming NICS requests (Or a representative sample of them.) against the watch list, for maybe a week or so, and the reporter doesn't understand the difference between "47 people did X" and "here's a list of 47 people who did X".
At least, they could do the study that way without violating the 24 hour rule.
When I read a news report on somebody doing something that's obviously moronic, I always try to remember that it might be the guy writing the report who's the moron.