Final answer:
The Original Classification Authority (OCA) line is the line in the classification authority block that will always appear on originally classified information but not on derivatively classified information.
Step-by-step explanation:
The line in the classification authority block that will always appear on originally classified information but NOT on derivatively classified information is the Original Classification Authority (OCA) line.
This line identifies the agency or individual who has the authority to originally classify information. It indicates that the information is being classified for the first time and has not been derived from any other classified information.
In contrast, derivatively classified information is classified based on information that has already been classified by an Original Classification Authority (OCA), so this line is not necessary.