Many in Pakistan also believe that 1962 was the right time when Indian troops were engaged in NEFA. Field Martial (self proclaimed) Ayub Khan was the President of Pakistan and his press secretary Mr. Altaf Gauhar (now late) has shed some light in his book "Ayyub Khan, fauji raj ke pahle das sal". According to Mr. Gauhar, Pakistan dared not to enter its troops in Indian Administered Kashmir because:
There was a secret military pact signed between the USA and the India according to which USA were to help India if India was in the state of complete defeat in the hands of Chinese.
President Canady's regime had warned Pakistan not to take advantage of the NEFA situation and not to open up another front for the Indians.
According to Mr. Gauhar, had Pakistan had entered its troops in IAK, US bombers were soon to be seen in the Pakistani Skies.
That is all I know, and from Mr. Gauhar's book. Even though I was never able to confirm this secret India-US defense pact of 1962. Maybe some other members have better information on this subject.