Article 14 of the GDPR mandates that data controllers provide specific information to data subjects when their personal data is obtained from a source other than the data subject themselves. However, Article 14(5) lists specific exemptions to this obligation. Article 14(5)(a) explicitly states that the controller is exempt from providing this information if "the data subject already has the information." This exemption prevents redundant communication and acknowledges that the core transparency principle has already been satisfied if the individual is already aware of the processing details.

B. The phrase "too problematic" is vague and does not meet the specific legal standard of "impossible or would involve a disproportionate effort" as required by GDPR Article 14(5)(b).
C. Disclosure of third-party data is not a recognized exemption under Article 14(5). The information required under Article 14 typically concerns the processing itself, not the personal data of other individuals.
D. Implementing appropriate technical measures is a fundamental obligation for all data processing under GDPR Article 32; it is not an exemption from the transparency requirements of Article 14.

1. General Data Protection Regulation (GDPR) (EU) 2016/679:

Article 14(5)(a): "Paragraphs 1 to 4 shall not apply where and insofar as: (a) the data subject already has the information;" This directly supports the correct answer.

2. European Data Protection Board (EDPB), Guidelines on Transparency under Regulation 2016/679 (WP260 rev.01), Adopted on 11 April 2018:

Page 26, Paragraph 68: "Article 14.5(a) provides that the obligation to provide the information listed in Articles 14.1, 14.2 and 14.3 does not apply where and insofar as the data subject already has the information. The controller bears the burden of proof in this regard." This guideline confirms the exemption.

3. Kuner, C., Bygrave, L. A., & Docksey, C. (2020). The EU General Data Protection Regulation (GDPR): A Commentary. Oxford University Press.

Commentary on Article 14, Section 14.88: The commentary explains that the exemption in Art. 14(5)(a) applies when it can be demonstrated that the data subject has received the specific information required by Art. 14(1) and (2), preventing superfluous notifications.