When senior managers are unaware of a deliverable, it indicates a communication gap that needs to be addressed promptly. The project manager should meet with these stakeholders to review the project charter, which includes information on all key deliverables. This action aligns with the PMI's principles of stakeholder engagement and communication management, ensuring that all stakeholders have a clear understanding of the project's objectives and deliverables123. It is also consistent with the practices outlined in the Business Analysis Body of Knowledge (BABOK), which emphasizes the importance of stakeholder engagement and the need for business analysts to facilitate clear communication about project requirements and deliverables456. References: = Project Management Institute's resources on project communication and stakeholder engagement123, and the Business Analysis Body of Knowledge (BABOK)456.