When working on complex problems in complex environments, it is difficult to fully predict all future needs and the best solutions will emerge as the work is being performed.

Product Backlog refinement is the act of adding detail, estimates, and order to items in the Product Backlog. This is an ongoing process in which the Product Owner and the Development Team collaborate on the details of Product Backlog items. During Product Backlog refinement, items are reviewed and revised. The Scrum Team decides how and when refinement is done. Refinement usually consumes no more than 10% of the capacity of the Development Team. However, Product Backlog items can be updated at any time by the Product Owner or at the Product Owner's discretion.

The Product Owner is responsible for maximizing the value of the product resulting from the work of the Scrum Team. One of the ways to do this is to order the Product Backlog in a way that reflects the flow of value to the stakeholders and customers. The Product Owner can use various factors to order the Product Backlog, such as value, risk, dependencies, learning opportunities, and feedback loops. However, sometimes the Product Owner may face challenges or constraints that affect the ordering of the Product Backlog, such as external dependencies, market changes, technical issues, or stakeholder requests. In such cases, the Product Owner needs to balance between delivering value and managing risks. The Product Owner may need to adjust the Product Backlog ordering to account for these factors, but not at the expense of compromising the value delivery. In this scenario, the Developers are waiting for an external supplier to deliver a specific product component that they need to integrate and use. Without that component there will not be enough work in the next Sprint to occupy the full team. They ask their Product Owner to re-order the Product Backlog. The Product Owner asks the Scrum Master for help. A good advice for the Product Owner would be to tell them that their primary concern is the flow of value reflected in the ordering of the Product Backlog. Timeline of the flow might be influenced by such dependencies and require some level of Product Backlog re-ordering.
This advice would help the Product Owner to focus on delivering value while also considering the impact of the external dependency. The Product Owner could work with the Developers and stakeholders to identify and prioritize other valuable work that can be done in the next Sprint without relying on the external component. The Product Owner could also communicate with the external supplier and try to minimize or eliminate the dependency as much as possible.

Working software is the primary measure of progress. Scrum is based on empirical process control theory where delivering working software frequently and measuring the impact helps the Product Owner maximize opportunity for the business to deliver value.