This page lists the limitations of this redundancy checker, as far as known by the author

Known false positives

A false positive is a false alarm: a rule is reported as being redundant, while it actually isn't redundant.

Known false negatives

A false negative is a rule that is redundant (and can be detected as such with the given input), but isn't reported

Ignored rules

Ignored rules are rules that the redundancy checker skips before even trying to find matches. Say, false negatives without the need for a second filter.