So Boeing had better make sure that when the structure is hit and no mark is left, the residual strength is going to last until the deepest NDT inspection has taken place.
I attended a RAeS lecture about the 787, a few months ago (last year?) and the speaker, a guy from Boeing's sales & marketing, not engineering, said something along the line that Boeing will guarantee that "if it looks undamaged, it is undamaged", i.e. a satisfactory visual inspection is enough to rule out any possible damage.
I'm not sure how firm this commitment was, possibly as firm as date of the first flight...