Section 320 IPC ko Samajh Nahin Aaya

I'm still trying to wrap my head around Section 320 of the IPC. Is it just me or does it seem like a mess? It defines 'grievous hurt' but then there are so many exceptions - Section 320(2) says it doesn't include permanent privation of the sight of either eye, yet Section 320(3) says it does if the sight is permanently destroyed by the act. But what if the person was already blind before the injury? Does that mean it's not grievous hurt? And what about Section 320(4) - it says it doesn't include permanent privation of the hearing of either ear if the person was already deaf? Ye sab kaisa hain? It feels like the legislators were trying to cover all bases but ended up creating a contradictory mess. Can anyone clarify this for me?