The purpose of the Controlling a Stage process in PRINCE2 is to monitor and control a stage within its authorized tolerances. During this process, the Project Manager assigns work, monitors work progress, deals with issues, reports stage status to the Project Board, and takes necessary corrective actions to stay within the stage's tolerances. References: PRINCE2 Foundation official documentation and study materials.

Within the context of a PRINCE2 quality review meeting, the role of Chair is recommended and crucial.
The Chair's responsibility is to ensure that the review meeting is conducted methodically and remains focused on its objectives. This includes leading the discussion, ensuring that all issues are aired and discussed properly, and that the meeting runs within its allocated time. This role is distinct from that of the Project Manager, Assurance, and Producer.References: PRINCE2 7 Foundation study guide and official documents.

In PRINCE2, the Senior Supplier role is responsible for the quality of the specialist products delivered by the project. This role represents the interests of those designing, developing, facilitating, procuring, and implementing the project's products, ensuring that the products meet the required quality standards and fit for their intended purpose. References: PRINCE2 7 Foundation Handbook and official training materials.

According to the 'continued business justification' principle in PRINCE2, project benefits must be aligned to the business objectives. This alignment ensures that the project remains viable and relevant throughout its life cycle, and that it contributes to achieving strategic goals. References: PRINCE2 Foundation Training Manual; PRINCE2 2017 Foundation handbook.

By organizing a workshop with project stakeholders to define the detailed requirements for project outputs, the team manager is applying the PRINCE2 principle of "Focus on Products." This principle emphasizes that a project's primary focus should be on product definition, delivery, and quality requirements, which are crucial for achieving project success and user satisfaction.References: (PRINCE2 7 Foundation Handbook, AXELOS)