Hi eBay community

I have sold two items to a buyer. The 2 items have been delivered. The buyer has acknowledged this. But the tracking status remains as SENT and not updated to DELIVERED. The items were both in the same package. Standard Australia Post with a tracking ID. Why hasn't the status been updated to DELIVERED? Does the buyer do that or does Australia Post do that? I've asked the buyer to update and they say they can't / don't know how? Any thoughts? Does it matter if the status remains as SENT forever?

thanks

Tim