Some aircraft use control surfaces that are driven indirectly through a flying tab system -- this is used to aerodynamically boost control forces, and works well enough in the normal case. However, it is possible for such a system to mechanically fail in a way such that the flight control and the tab are both capable of free movement throughout the control range, but the control surface does not respond to the tab's movement correctly, causing a reduction or loss of control authority.
How can a pilot catch this type of failure in a preflight or during a flight control check? "Full and free" clearly isn't enough to catch such a failure, since the tab will move freely throughout the entire control range even if the actual surface is frozen in place. Is it the case that the only way to catch this sort of failure is to disengage the gust locks and then try to move the control surfaces by hand through their full movement range? Should the control surface position be fed back to cockpit instruments in these aircraft, or is that already a requirement/feature on such types? Is it common practice or required in a "full and free" check to verify surface followup on such cockpit instruments when they are fitted?