According to the Professional in Business Analysis (PMI-PBA)® Guide, a requirements traceability matrix is a table that links requirements to their origin and tracks them throughout the project life cycle. A requirements traceability matrix helps to ensure that all requirements are addressed by the project deliverables, and that any changes to the requirements are reflected in the project scope, schedule, cost, quality, and risk. In this scenario, the project manager should review the requirements traceability matrix with the concerned stakeholder to verify if the requirement in question is indeed missing or not. This would help to clarify the source, scope, and status of the requirement, and to identify any gaps, inconsistencies, or conflicts between the requirements and the deliverables. This would also help to avoid any misunderstandings, miscommunications, or assumptions that could lead to stakeholder dissatisfaction or project failure. Checking the approved list of requirements, working with the stakeholder to improve the acceptance criteria, or discussing additional requirements are actions that should be taken after the review of the requirements traceability matrix, not before. These actions do not address the root cause of the situation, which is the possible discrepancy between the requirements and the deliverables. References: (Professional in Business Analysis Reference Materials source and documents)

Professional in Business Analysis (PMI-PBA)® Guide, Chapter 4, Section 4.3.1.3

A Guide to the Project Management Body of Knowledge (PMBOK® Guide) – Seventh Edition, Chapter 5, Section 5.2.2.3

The Standard for Project Management – Seventh Edition, Chapter 3, Section 3.2.2.3