Complaints are also a part of the quality systems. There are a number of parts of the procedure when dealing with a complaint. Defining the responsibility of who is going to do what when a complaint is submitted, and how it's going to be dealt with - including developing the investigation report - will dictate how an investigation will take place when dealing with a complaint.
Change control is something that an inspector likes to see throughout an inspection. The SOP defines who is responsible for dealing with change controls as they come though. The associated change control documentation can track where changes were made. There are various levels of change - minor or major - that will dictate what kind of documentation a company is going to have for the change control.