Furthermore, the data may be static, but de-anonymization capabilities are not and may improve over time to identify someone. For example, if they're tracking

Furthermore, the data may be static, but de-anonymization capabilities are not and may improve over time to identify someone. For example, if they're tracking all instances of various ailments seen by some doctor in some time period. Suppose you are the only person of a given age and gender with that ailment, so that bucket would one entry for anonymous you. Fine. But then suppose the aggregating party begins to buy and correlate against credit card and location records that place you at the doctor's office in that time frame, bingo, they have a match to tie all three data.