I would guess it's the opposite of "bad best-practices", namely that there are no common best practices. Everyone intuitively understands how black-box redaction works, but the ways inadequate redaction fails is a bit technical and not intuitively obvious, so it's a task that's ripe for ignorant overconfidence.
Actually, it is quite weird, I wonder if some bad best-practices have been circulated.
It would be really nice if legal documents were prepared in some sort of standardized markup-like language.