Tell me if my order of operations is wrong but what I've been doing is to check the vectorscope first for illegal colors, then use secondary color correction filter accordingly. Then I check the YC Waveform for a safe IRE range and adjust levels accordingly.
I think using seconadary cc is the wrong tool for the task of legalising broadcast video.
A broader brush can be applied to legalising Luminance and Color Luminance in individual channels.
That is why I suggested LEVELS. ( Waveform and RGB Parades.)
I use Levels for all my broadcast work and they pass the very strict broadcast QC we under go.
As I said...applying levels automatically clips and this is the start point. I drop everything from there a little and then work on individual channels. ( Usually Red is the culprit).
The Broadcast Filter is aweful , does not do as good a job and has limited control...so I never use it.
It actually can cause issues because of the way it works. ie luminance / chroma buzz in areas that get controlled.