The crucial piece is your link is:

> 4To ascertain whether means are reasonably likely to be used to identify the natural person, account should be taken of all objective factors, such as the costs of and the amount of time required for identification, taking into consideration the available technology at the time of the processing and technological developments.

This has been interpreted that any objectively possible way to de-anonymize is reasonable. In particular, considering that all the data of the organization doing the anonymization can be used to try to de-anonymize.