I'm not sure if every center does this, but here they expect us to call the building for packages we can't find. Give 'em the address and tracking number and they can look up whether that package was scanned and loaded on-car. It usually only takes a minute or two and can be less of a pain in the ass then shuffling through 100's of pkgs looking for that one piece that was never loaded to begin with.
It's not fool-proof, though, as the loader may've loaded it without a scan, but it helps most of the time.