I still assert it's only a matter of cross-correlating that data with something else.
I don't know what kind of data you're working with, but for the sake of example let's assume you're handling buying records from supermarkets. You obviously hashed people's ClubCard/credit card numbers. But let's say I get hold of the data from an ALPR on a street near one of the markets. Would correlating that with your database not help to deanonymize a lot of your data?
My point is - as the data collection of every kind increases, for every dataset you have anonymized, there will be a lot of other data sets of all sorts that can be used to deanonymize back yours.
Of course there is.
I work in a business today that collects highly personal consumer data and does advanced analytics. We strip personally identified invention once the data is brought in so there is technically no way to to deanonymise it.
We are hardly unique.