Well... I will try to put it in a different light. A cross functional product team must have all the knowledge to complete the tasks they are given. There is no way agile is going to work for you if there are 5000 people with a saying on your day to day tasks.

If there are a few stakeholders outside the team it's really the PO's job to represent them. If you need to know if the task is complete you ask the PO and she should made the call. It’s simple really