So I can say with certainty is that USPS and customs inspectors don't seem to work with any rhyme out reason.
Case in point for USPS: I recently broke my cell phone got an insurance replacement, then sent the old one back to the insurer in the box they provided for me with the first class label and tracking number with barcode neatly attached.
20 days later I get a letter from the insurer saying, "You were supposed to return your broken device and did not, now you owe us $900). They ran the tracking number, it showed inactive. I filed a useless claim with USPS that ultimately said, "Whelp, we can't find it, sorry. But thanks for using USPS."
2 months later, just out of curiosity, I ran the tracking number to give it just magically appeared at the insurance company 2 days earlier, after 61 days of being missing.
Case in point for customs: I ordered Etizest last fall and it had it to "inbound into customs" then just stopped moving. 2 weeks later, it pops up as out for delivery and when I run the tracking number all the places it had been for the past 2 weeks were suddenly there. It was like they had a massive glitch in their system that causes lag or the scanners get confused and don't properly record information. Who knows.
My current order from eastern Europe says it's being delivered tomorrow, but its last scan was on May 6th and said, "processed through ISC NY inbound into customs".
The whole system needs to be rebuilt from the ground up.