What must altitude information in data blocks reflect?

The altitude information in data blocks must reflect the actual clearance issued. This is critical for ensuring safe aircraft operations and maintaining proper separation between aircraft in controlled airspace. The actual clearance represents the altitude at which air traffic controllers have authorized the aircraft to fly, which is based on operational, safety, and regulatory considerations.

By using the issued clearance, air traffic controllers can maintain a reliable and consistent framework for monitoring and managing aircraft movements. This ensures that pilots are operating under the instructions provided by air traffic control, which is vital for maintaining safety in the airspace system.

The other options do not provide the necessary accuracy and regulatory compliance required for aircraft operation in controlled airspace. Suggested altitudes or averages do not hold the authority that an actual clearance does, which is essential for keeping track of aircraft positions and ensuring effective air traffic management.