Qifel:
I recommend that you do not look at the Process Groups as a linear function. It is far better to view the Project Management process as a large, continuous loop. For example, if you identify an area that needs bolstering, you would naturally go to the starting point of that particular process group.
"Initial" stakeholders are usually identified during business case writing (or "pre-project" as it were). However, as the PM Plan and other subsidiary plans are being developed, other stakeholders to the project will be identified, and as they are, the entire Manage Stakeholder knowledge area will be performed.
Hope that helps.
Harry