In the end...do you really think it matters?
Whatever stealth is, do you think customs actually believes that?
They aren't stupid...they seize it, and if it is valid you can go to for release.
These packages that make it through aren't inspected truly?
I think it's just odds of packages clearing or not based on volume/inspection day.
Just my thoughts..
I've got a few clients that are with customs here in canada. They have pics of drugs for comparison, and if something leaks or has a powder on /in a suspected package they can test it, but first it has to be suspicious enough to get to that point.
They have no idea of many things. You can very easily slap a label stating b12, or whatever on a vial and they have no choice but to let it go (unless its packed in with other obvious violations).
Most packages that get seized have either leaked or sound like pills, come from known /tagged countries, or are suspicious and x-rayed, then opened if they look like a box of pills /vials etc.
There just aren't enough workers to catch and inspect everything, so if stealth packaging can get your goods to you if your package does happen to get inspected, no matter how they do it, it's beating the system.