What is a tracking number?
How to find your tracking number?
You can track your international package in both sending AND receiving countries. A quick and painless how to.
DHL International Tracking Number not valid with Canada Post?
Package from Korea not delivered; Tracking for registered mail stops after package reaches US -- who to turn…
If someone had scanned it accepted, or scanned it at any subsequent points, it should have the tracking displayed.
My guess is USPS has not received it yet. The fact that it has left Korea does not mean the next place it traveled immediately was the USA. It could go through China or Japan or be on a slow boat in the Pacific Ocean. It could be held up by customs somewhere.
With the tracking number RM160063414KR, it would require a signature for a delivery scan to be completed. So if it was scanned it is unlikely it was misdelivered, as usually you say "I have a package for So-and-So, would you like to sign for it?". People would say, "There is no one by that name here." So if you are assuming a misdelivery, than you are also assuming the carrier did not scan it delivered... in which case you are looking for evidence of a scan that does not exist. That is a hopeless undertaking.
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