Dilemma in S. 29 Evidence Act aur BSA

Main confuse feel kar raha hoon. Papa ne mujhe tell kiya hai ki Section 29 Evidence Act ka matlab yeh hai ki yadi ek evidence ki authenticity prove karni hai to court ko uska chain of custody check karna hoga. Lekin BSA ka Rule 18 bhi ye kaha hai ki court ke paas evidence ko verify karny ke liye chain of custody pehle kaafi hi reliance karna hoga.

Mujhe laga hai ki ye dono sections ek hi baat keh rahi hain, lekin main samaj nahi sakta ki kya difference hai. Kya main galti se think raha hoon? Aur kya yeh dono sections ka application kahaan hota hai? Main to confused ho gaya hoon. Kuchh batain, please!