What is the definition of 'Carpet Area' in Mumbai?

I am writing on behalf of more than 50 flats in City of Joy, Nirmal Lifestyles, Mulund, Mumbai.

We were promised a flat of 726 Sq ft in carpet area (Saleable Area 981 Sq ft) by Nirmal Lifestyles. We find that with precise measurements that do not include the walls, the carpet area is 46 Sq ft less than what was promised. Our question is:

1) Is the 'skirting area' of the tiles included in carpet area under BMC definition?

2) Since the agreement doesnt have a precise definition of 'Carpet Area', who is responsible for the same? The BMC or the builder?

3) Are we entitled for repayment of value of the 'cheated area' at current prevailing rates or we have to get the agreement amended with the lesser area? Can we pull up the builder in court for the same.

Thanks in advance for your replies.