As we all know around here, national aviation authorities put out Airworthiness Directives mandating certain changes be made to aircraft during their service life so that the aircraft can stay airworthy. The paperwork for these ADs is part of the aircraft logs, and thus stays with the aircraft for the life of the aircraft.
However, just because an AD is marked as complete and closed out in the paperwork does not necessarily mean it has actually been completed. This was a causative factor in the Omega flight 70 mishap, where an engine fell off a 707 shortly after rotation and damaged the plane to the point where it could not climb out. The investigation revealed that although the applicable ADs were marked complete, the upgraded part required to be installed to close the ADs out had not been installed on the mishap aircraft. Instead, a prior owner had marked the AD at the time complete when it had not actually been fully closed out.
How can an aircraft owner ensure that the ADs that the paperwork says have been closed out on an aircraft have actually been closed out and not simply pencil-whipped? Are such verifications ever performed during maintenance or inspections (including pre-/post-sale inspection), or is the paperwork trusted absolutely? Furthermore, how can an inspecting mechanic accurately determine the completion status of ADs? (For the 707 AD in question in the Omega 70 mishap, this could be done with a small template and some mechanic time inside the pylon, but I suspect some ADs aren't that easy...)