International tracked shipments have
bar codes that look different from tracked US shipments. Some clueless postal people neglect to scan.
I have
had envelopes delivered and then received on the next day an email from the Postal Service saying not to worry, the package is
still moving through the system!
I have
had envelopes sent to the wrong post office, sent back to Europe, and returned to the sender, with no tracking updates after the arrival in the US.
After a month with no movement it is a
good idea to contact the seller and ask if they can track it through their postal authorities. This lets the seller know there is a problem without jumping to any conclusions.