Every province has its flag. No reason why AJK shouldnt either. Flag of Punjab.
Balochistan flag
Heck in Europe even many small towns and cities have their own "coat of arms" and flags. This is the coat of arms of the city I live in:
I see nothing wrong in different provinces or regions being able to have their own flags, practice their own cultures, speak their own languages. Unfortunately 71 has left many Pakistanis traumatized I think but we need to get over it. East Pakistan was an anomaly. As Anatol Leivin put it a "freak of history". It was bound to break apart. However no other part of Pakistan will now break apart as we form one contigious country with ethno-linguistic groups who have resided next to each other for millenia and a strong military to maintain this unity and nuclear weapons in the case of a foreign invasion 71 style.