1. Partial penetration of the blade of a knife
2. Forceful stabs to structures like abdominal wall & lungs  where  there may be indentation of the tissues result in the blade of the knife penetrating to a greater depth [x+ y] than the length of the blade [x] causing a stab wound which is deeper [x +y] than the length of the blade [x]
3. Stabs with a knife with no hilt guard