Complete final contract performance reporting and verify product is done in Close Procurements.

The preliminary scope statement contains a preliminary version of the things you see in the scope statement. It shows you an initial description of the work that needs to be done, so that you can begin planning. It does not contain any changes yet, because when you write it, you haven't created any deliverables yet, so there's nothing to change. Another way to think about it is that you build the preliminary scope statement at the very start of the project - that's why it's in the Initiating process group. You don't run into any requested changes until you start planning the project, so that's an easy way to know that your requested changes aren't part of the preliminary scope statement.