It appears there is a spectrum of de-identification tools, some being better than others. https://en.m.wikipedia.org/wiki/Data_re-identification https://en.m.w

It appears there is a spectrum of de-identification tools, some being better than others. https://en.m.wikipedia.org/wiki/Data_re-identification https://en.m.wikipedia.org/wiki/Data_re-identification I suspect that the more data they have for a particular patient (many visits over multiple years) makes the re-identification process easier. The article mention financial data, if dates and amounts of charges aren't masked or altered that could be cross-referenced with another data source to deduce the person's identity.