Things can get bent or cracked, and the cracks can be internal. They can also be in the crankcase... That's why one has to NDT the whole engine.
In the past, and it may still be true, Lyco allowed an engineer to countermand the shock load inspection if a) the engine did not totally stop in the strike AND b) the crankshaft flange was still running true. I imagine many took advantage of this but it's IMHO very poor risk management, especially in a SE.
Many prop strikes are unreported and unlogged. One clue might be prop hours differing from engine hours, but somebody with a brain will fit a new prop (to replace the damaged one) and transfer the S/N from the old one, or just change the blade(s). Then it breaks years later....