Yeah... Pakistan is free to celebrate any number of military defeats.. even December 17..
I don't understand your reference to Shastri's death. Don't people die of heart attack in Pakistan??
I don't know why Pakistan celebrates Sept. 6.
We need to understand the objectives and achievements of each country to analyse their performance in 1965.
Pakistan:
Objective > Capture Kashmir, Defend Lahore
Achievement > No, Yes
India:
Objective > Defend Kashmir (capture of Lahore was not the objective, attack on Lahore was in support of the main objective of defending Kashmir)
Achievement > yes
Pakistan was barely able to defend Lahore by flooding the canal and slowing down the Indian advance. By Sept. 6 Pakistan had forgotten all about capturing Kashmir, its main objective of starting the hostilities, and was struggling to defend its 2nd largest city. Its ammunition stock was almost over and its capability to fight for few more days was exhausted, whereas India had the capability still left to carry on the war for few more weeks, if the global powers had not forced the 2 countries to accept the ceasefire.