They only "flag" packages at local hubs. That's why some packages get thru and others might get tagged. Customs gets lucky but the real pain is when Customs notifies your local post office.
That's why PO Box XXXXX might never work again but a different address in the same town will still work.
I had a package nailed from Japan a few years back and the postal inspector explained it to me
Sometimes, the local branch will flag a name but not an address. You can use the same address with a different name