When you stress a part, engine, transmission, rotor blade, cross tube, ect..... it probably won't fail right away. Chances are it will fail much later on some poor unsuspecting soul who is just out doing his job within all rules and guidelines. That is why it is good to work with trustworthy folks who fly and maintain the machines. If you are not sure if something was normal or abnormal, discuss it with your mechanics and pilots.
Not sure if this applies to your question. Several "firm" landings could be cumulative.