MJB - The population of the Brown Rock Chat was found only within the Lahore area maybe until recently as 20-30 years ago. Since then it expanded West rapidly. The populations you mention are recent extensions. My family originates from the Northern section of the Attock disrict - on the border of Khyber Pakhtunkhwa formerly known as the North West Frontier Province. The first time I saw this bird in this area was in January 2011 - granted I only visit the region every 2-3 years but I saw 3. In March 2014 I saw them quite regularly and they were singing and breeding. My uncle mentioned that these birds have slowly moved into this area over the last 8 years. Now they are firmly established. I saw 1 in Peshawar City in March 2014. In January 2016 I saw them at Takht bhai in Mardan District and in the vicinity of the Terbela Dam. In fact it is spreading North and has been recorded in Balakot. It is firmly established in the Peshawar Valley and has almost certainly advanced into Afghanistan but just needs to be seen there. It has also been seen and recorded in Dera Gazi Khan and Dera Ismail Khan. In Pakistan no photo as been obtained from Sindh yet.
Most of the sightings are from Urban areas, towns, villages, ruins, new developments - they thrives in these areas. I wonder if one will be recorded in the WP in our lifetime?