It's not the job of FAA inspectors to inspect what the workers actually do either announced or unannounced.
We have to trust workmanship in all parts of our lives. Where it is critical we develop and implement procedures which are in place over long periods of time covering numerous work processes. Lack of procedures/processes don't really lend themselves to being covered up. Missed inspections or plain human error are there to be seen by all who look.
Fortunately the aircraft itself has multi layers of tolereance to single system screw ups.
I do expect that both FAA and the operator may announce a closer look at the maintance processes that let this happen.