If they knew what some of the stealth shipping methods look like, they could identify some packages, but there's no way they could know that they are identifying all the packages, or even most of them. There's no way for them to know how many other drug packages are in the mail system. Even if they identified 100% of drug packages, they could only be identifying 10% for all they know. Another way to put it is that they could have a low false positive rate but a high false negative rate, and the only way to know their false negative rate is to inspect all packages, which they don't do. Those claims sound like typical LE bluster. They find one package and say "we're one step ahead of the drug dealers", even though stats on this site show that 96.5% of packages get through.