I actually began to have my doubts about the census after reading all the complaints I read - in particular with regards to Karachi. I then did my own lay observations like satellite imagery of Lahore and Karachi but the spread of the built environment proximated to the figures given by the census. There appeard to be no slip between Karachi and Lahore from what I could see but with all the hue and cry emanating from Karachi residents my doubts persisted - given that we had a PML Nawaz Sharif federal government and also in power in Lahore with Shebaz. It did seemed possible given Pakistan and proclivity for "fudging facts" the PML government had skewed the results in it's favour to the loss of Karachi.
I was also told by many members from Pakistan that the soldiers just stood guard and the actual count was done by civilian PBS enumerators. Thus having the army their did not really make the count immune from being distorted and did not really carry Pakistan Army 'seal of approval' as it only provided security. However after reading this article I honestly was surprised that in face we had two headcounts in Pakistan. One done by the army. I am surprised non of the detractors mentioned this - indeed they reduced the armies role to just "observers".
Thus my surprise after I read this article. I have no doubts now about the accuracy and consider it as good as your going to get in Pakistan. Karachi's population is correct as far as I am concerned.
@Joe Shearer Noted and thanks!