I work for an Australian Bank. We had an internal competition where they didn't sanitise the data for this competition well enough. After a week of analysing the data one of the people in competing in the competition knew who's data we were looking at. It was a friend of theirs.

All identifying information had been removed/sanitised, they could tell from looking at the spending habits.

I disagree with your statement.

what if there are only 5 'people like me'. Or even 1 or 2.