NPCs do have cloaking devices.
Ever been to a "I can't believe that worked!" USS?
Drop in, nothing on sensors.
Cargo/Data/Wreck Spawns.
Nothing on sensors.
Fly in Closer.
Use Debug camera for 360° visual check. Nothing.
Open cargo hatch. Nothing.
Move Even Closer.
2 Anacondas, and 4 Vulture appear, 500m away. Directly in front of you.
No waking in, just 'pop' and small fleet appears out of nowhere.
Cloaking Tech!
They should either;
Spawn just outside of your Sensor range, and fly in fast.
Or, wake in nearby, but in sensor range.
Or be there the entire time, stationary, in silent running so you can visually spot the trap, if you're paying attention.
Or, my favourite, have a single ship in silent running, lurking nearby. And after a while, if you approach the cargo, it calls for its gang to drop in.