As I said, I'm not a technical expert, but it does seem to me, from the evidence, that such a notion is very hard to actually obtain in practice. There are ways of taking care, and taking more care with data analysis especially. And don't forget that I mentioned each of the stages. It's not only the collection, the gathering of those data in the first place. The analysis is critical, and within those forms of analysis anonymity may also be compromised, right through to the uses of those data.
I have great doubts that there is a real sense of anonymous data.