If tracking shows delivery all you need to do is put the tracking number in the cases before the "due date" in the messages you received for the cases. Make sure to put the tracking number in the cases even though it is probably already attached to the item(s). This is an important frustrating thing that I see in other threads folks have not done and not physically putting the tracking number in the cases themselves before the due date (and if it says December 10th it means Dec 10 at 12:01 AM I learned this the hard way) will cause the cases to close in the buyers favour and give you defects which you do not want.
I don't see any neutral or negative feedbacks on this account yet, but if one does come along, put your feelings aside and simply put the facts in the reply to the feedback that the tracking shows item was delivered to the buyer.