The task of proper anonymization is harder than it looks. Yet another example:
It turns out, though, that those redactions are possible to crack. That’s because the deposition—which you can read in full here—includes a complete alphabetized index of the redacted and unredacted words that appear in the document.
We Cracked the Redactions in the Ghislaine Maxwell Deposition (via Schneier on Security)
This seems to be a corollary of Schneier’s Law: Any person can anonymize data in a way that he or she can’t imagine breaking it.
Although the truth is most don’t even try to break their own work.