A police force failed to report more than half of knife crimes committed, it has admitted.
Between 2016 and 2018, there were 1,322 knife crimes not recorded as such, Sussex Police's figures show.
A "semi-hidden" box on the crime recording system has been blamed for the omissions, which the force said was being "put right".
Sussex Police and Crime Commissioner Katy Bourne said the recording of knife crimes was "under close scrutiny."
In 2016, 296 crimes involving blades were recorded by the force when the real number was 665.
By 2018 there were 827 knife crimes committed, but only 298 were recorded as having involved blades.
The information was shared by Deputy Chief Constable Jo Shiner during a meeting with the police and crime commissioner, the Local Democracy Reporting Service said.
Ms Shiner said: "When there is a crime which is a knife-enabled crime, then there is a box officers need to tick in order to positively say a knife was involved."
She said the box was "almost semi hidden" and had been missed by officers.
"We're putting that right," she added.
She said knife crime in Sussex was still "relatively unusual" and it was "still a very safe place to live".
Ms Bourne said she was keeping the recording of knife crime "under very close scrutiny".