Which of the following is an authorized source for derivative classification?

A properly marked source document is an authorized source for derivative classification because it contains specific classification markings that indicate how the information should be handled and classified. These markings serve as a guide for individuals tasked with derivative classification, ensuring they adhere to established classification protocols and protect sensitive information appropriately.

In contrast, unverified reports lack the necessary reliability and official approval needed to justify classification. Verbal briefings from superiors, while often informative, do not inherently provide the documented evidence or classification markings required for derivative classification. Increased speculation from team members lacks any official status and does not offer the authoritative basis necessary for determining how information should be classified. Thus, relying solely on properly marked documents is essential for maintaining the integrity of the classification system.