Which document serves as notification to DAAS or a supply source that the total number of indicated documents was not received?

The correct choice is the APX document, which serves as a notification to the Defense Automated Addressing System (DAAS) or a supply source indicating that the total number of indicated documents was not received. This document is vital in the supply chain management process as it helps to identify discrepancies in the paperwork associated with shipments.

The APX essentially acts as a communication tool to inform relevant parties of any issues regarding the documentation, ensuring that all stakeholders are aware and can take necessary actions to resolve the situation. By referencing the correct document, processes can be streamlined, and the risk of further errors or misunderstandings can be minimized in military logistics.

The other options do not represent this specific function related to notifying DAAS or a supply source about missing documents in a shipment scenario. Each of those serves different roles within the MILSTRIP framework but does not pertain to the acknowledgment of undelivered documents as clearly as the APX does.