The customer's acceptance closes the correspondence, not the complaint. Keep the complaint open on the log until the corrective actions have met the criterion set before they went in, over the agreed window, using the effectiveness worksheet (AQL-B08). Then send letter 4 with the result, end the temporary checks that were waiting on it, and close the line.
If the criterion is not met, say so: reopen the corrective action, tell the customer, keep the temporary checks, and go back to the cause. A reopened record with an honest letter does far less damage than a closure that turns out to be premature.
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A management aid, not certification or a registrar audit. Using it does not by itself show conformity to AS9100D or any other standard, and your customers' requirements may add to it.
Clause numbers refer to AS9100D (SAE AS9100 Rev D) unless another document is named. The standards' text is not reproduced here: use your own licensed copy.
Aegis Insights are our own guidance, labeled wherever they appear: how we approach this work, not a requirement of any standard or customer.