In his life, Adi Shankara travelled within Indian subcontinent to teach the philosophy of Advaita Vedanta. He even went to Benaras and then Mithilanchal (Bihar) to defeat Mandal Mishra. Adi Shankara established four mathas at Davarka, Jagnaath Puri in Orissa, Sringeri in Karnatka and in Badrinaath in Utrakhand. Even if there is debate whether he established these mathas or inherited from others, there are no sources claiming he tired to establish or inherit any such mathas in the area of modern Pakistan, Bangladesh, and any other part of old India. During his time (8th century CE), Arab had reached and established in Sindh, but still these regions were ruled by Rajput (the Soomra dynasty 1024-1351) for along time. Even Mahmud of Ghazni defeated the Kabul Sahi dynasty in 1011 CE. Therefore, it is surprising that why Adi Shankara did not travel to the modern Pakistan or Bangladesh to establish such Mathas even if there are 5 Shakti Pithas in Bangladesh, 3 in Nepal, one in Pakistand, one in Tibbet and one in Srilanka.
So, it suggests that Adi Shankara had an idea of the division of India into modern India, Pakistan and Bangladesh.

Parmit Singh Dhurandhar