There are several components to a plane that can be damaged (either incrementally or totally) either by toggling failures through the "Aircraft" tab or by damaging the component in-flight. I've been working on tracking damage of landing gear through a gauge, and in doing this I've noticed what appears to be a real lack of access to tracking the damage states of airplane components. In the whole simulation variables document, I can really only see tracking for engine damage - everything else is either partial (like landing gear, where I can track if gear are being damaged, but not the damage state/percentage) or simply missing (e.g. wingtip damage).

Is there some set of undocumented variables for these?

Is this akin to what Accusim are doing with their A2A series of aircraft? I do not have any of them but I believe they have some process of wear and tear and cumulative damage by poor pilotage.