http://www.thetrace.org/2015/07/gun-background-checks-nics-failure/
8. Adjudicated Mental Health: 18,678
Disqualifying mental health records form
the second largest body of records held by NICS. Simply receiving a diagnosis of a severe mental illness like schizophrenia is not enough to put an individual in this category a judge must
legally declare them mentally unfit to own a gun or involuntarily commit them to a mental institution.
Though NICS does have access to a large number of disqualifying mental health records, an unknown number still arent reported. In the case of Lafayette shooter John Houser, though a judge considered his severe mental health problems in 2008, doctors
did not recommend he be involuntarily committed, and even if they had,
Georgia law would have required the purging of any records of that commitment by 2013, before he purchased his gun.