Aloha,
There are far too many variables in order to properly figure out what might have occurred.
I have in the past hit a Yamato in the bow with every single torpedo from my Cossack before, but because every torp hit in the same spot I dealt VERY low damage levels and in fact the flooding is what dealt most the damage.
As people have stated above, parts can become damage saturated and seriously effect the damage that you can deal to a ship.
-Hapa