It's not often discussed, but the likely main goal of any boundary negotiation with India for China is to recover a fairly obscure piece of real estate called the Tawang tract. In February 1951, India (or rather the Governor of Assam) sent a small military expedition to Tawang and annexed it. British India had never ruled over Tawang and according to the source below the Government of India in Delhi had never instructed the Governor of Assam to annex it. Situated in the Tawang tract is a town and the Tawang Monastery, "one of the most holy sites for the faith of Mahayana Buddhism". While most of the rest of the entire Indian state of Arunanchal Pradesh is claimed as South Tibet, nobody seriously wants it. Occasionally, the Chinese Ambassador in Delhi might give an interview to Indian media and claim the whole thing. However, I believe Tawang and most importantly the monastery is the true goal. Similar to Indian claims over Azad Kashmir (Pakistan administered Kashmir), no one in India seriously wants to take control of the territory even if the gate was wide open. It would just be a huge headache without much benefit.
I wanted to bring up this bit of history and explanation about the likely negotiation position of China to better focus the discussion on whether any mistakes were made in 1962 in hindsight.