THE UCR (uniform crime report) does not necessarily cook the books, it just does not differentiate which homicides are justified...that way no one actually knows.
Now inaccuracies come from some Departments not filing or not filing on time each year, if required to do so.
The UCR statistics are complied from all City Police Departments and County Sheriff Departments with over a certain population number in the USA. The FBI usually is two to three years before posting the data, since it takes a while to assemble and get accurate statistics, according to what they receive for each year.
The article quotes the FBI instructions to the people who fill out the UCR forms.
It gives a definition of what they consider to be justifiable homicides.
That definition eliminates the vast majority of what a court or prosecutor would consider to be justifiable homicides.
I call that “cooking the books”.