If personal data has not been collected from the data subject, the controller shall inform the data subject thereof. Among other things, the information must disclose the name and contact details of the controller, the purposes of the processing of the personal data and the respective category. Detailed information can be found here.
Art. 14 par. 5 lit. B GDPR provides for an exception to the obligation to provide information if the provision of the information is deemed impossible or would require a disproportionate effort. The number of data subjects and the age of the data play an important role. According to Art. 29 of the Working Party on the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Protection of Individuals with regard to the Information. The result must be documented. Should the legal basis for an exception to the obligation to provide information exist, appropriate measures must nevertheless be taken to safeguard the rights, freedoms and interests of the data subject.