The Stakeholder Register is a critical document in project management that lists all stakeholders involved in a project, including their roles, requirements, expectations, and influence on the project. The fact that the leader of a user party was not included in the requirements collection communications suggests that the Stakeholder Register was either missed or outdated. This document should have been used to identify all parties with a vested interest in the project, ensuring their needs and expectations are considered during the requirements collection phase. An up-to-date Stakeholder Register is essential for effective communication and project success12.
References:
* "What is a Stakeholder Register?" - Project Management Academy1.
* "What is a Stakeholder Register in Project Management?" - The Knowledge Academy2.

One of the core values of agile is to deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter timescale1. This means that the project manager should seek ways to show the customer the value of the software as early and often as possible, rather than waiting for the final deliverables or a major milestone. By evaluating various delivery options, such as demos, prototypes, beta versions, or minimum viable products (MVPs), the project manager can get feedback from the customer and validate their needs and expectations. This will also help the project manager to prioritize the features that deliver the most value to the customer and align the team's efforts accordingly. The other options are not as effective as evaluating various delivery options. Asking the internal sales team to keep the customer informed of the delivered value may not be sufficient, as the customer may not be able to see or experience the software for themselves. Informing the customer about the progress and updating them on the final deliverables may not be enough, as the customer may not be satisfied with the outcome or may have changed their requirements.
Waiting for an important milestone to complete and then informing the customer of the progress may be too late, as the customer may have missed the opportunity to provide feedback or suggest changes. References:
* The 12 Agile Project Management Principles: Key Pillars of Agile
* Focusing on Customer Value with Agile Program Management
* What is Value-Driven Delivery in the agile world? - Whizlabs