from my understanding the defect report page updates every Thursday US so Fridays here. Then you are assessed over either a 3 monthly or 12 monthly period, your dashboard performance % page updates on or around the 20th of each month. So while there are defects coming and going over that period it is never going to be exactly correct as they all update differently.

On the dashboard performance % page there are also 2 tabs one that says your seller level is (current) and the second tab says projected seller level is (for the coming month) the 2nd one will give you some idea of what defects are dropping off and what new ones will be added.