Why would you bother about the missing part?
Because it has ended up in a location that will cause it to slowly wear into a vital piece of tubing or wiring, breaking through just as you are rushing to the airport (or delivery room), probably in either a major traffic snarl-up or major weather disturbance, or both.
Those parts that don't cause such overt damage will eventualy start to rattle or squeak - but only when you are driving, making it impossible to locate when stopped.