In my understanding the platforms are called 6/6A/6B or 7/7A/7B based on the type of train coming on it. if its a non-mmts , then they are 6/7 whereas for mmts it is 6a/6b/7a/7b to allow passengers to stand on the correct half of the platform. There are total 10 platforms only. In many stations 1a/1b are separate lines but are numbered so becoz of their short length