Portion markings in the IC, at least in the modern era, will include both the classification and a compartment. The compartment is specific to the collection method, i.e. SI indicates signals intelligence, TK indicates satellite data. Since those can reveal the source of the data, that reveals capabilities that the agency may not want to reveal, even if the data itself is no longer sensitive enough to classify.

Compartments are just for SCI. IC agencies do like putting all the classification markings on cafeteria menus, but they do non-SCI as well.

Both SAPs and SCI control systems can be unacknowledged/unpublished, and foreign releasability markings can easily be classified because they show that the country in question has an intelligence relationship with the US that covers a specific topic.

> Since those can reveal the source of the data, that reveals capabilities that the agency may not want to reveal, even if the data itself is no longer sensitive enough to classify.

Always 'member Trump and his release of a high resolution photograph from a satellite [1]. It took mere hours for people to work out which exact satellite was used to create the photograph and established a lower bound on its imaging capabilities.

[1] https://qz.com/1699833/what-we-can-learn-from-the-spy-satell...