Critical territories and lands in mapping Greater Old Khorasan :

North West Afghanistan (Spread through Herat , Balkh , Kabul , Ghazni , Kandahar ) (Heart of Khorasan)
North South East Uzbekistan (Spread through Samarkand , Bukhara , Shehrisabz , area between Ammu Darya & Syr Darya )
North East Iran (Spread through Nishapur , Tus , Mash'had , Gurgan , Damaghan)
South Turkmenistan [Mery Province ( Merv , Sanjan ) ]
South Kazakstan
North & West Pakistan [Malakand Division (Malakand , Swat , Dir , Chitral ) ]
North West tajikstan [Spread through Sughd province (Khojand , Panjakent)]

Expand of Khorasan :

~ Extended to entire Transoxiana (portion of Central Asia corresponding approximately with modern-day Uzbekistan, Tajikistan and southwest Kazakhstan. Geographically, it means the region between the Amu Darya and Syr Darya rivers) prior to 8th century AD
~ Extended to Soghdiana ( included territories around Samarkand, Bukhara and Kesh (Shahrisabz) in modern Uzbekistan & Khujand (Tajikstan) . Sogdiana lay north of Bactria, east of Khwarezm, and southeast of Kangju between the Oxus (Amu Darya) and the Jaxartes (Syr Darya), embracing the fertile valley of the Zarafshan (ancient Polytimetus). Sogdian territory corresponds to the modern provinces of Samarkand and Bokhara in modern Uzbekistan as well as the Sughd province of modern Tajikistan. ) in the north,
~ Extended westward to the Caspian Sea,
~ Extended southward including Sistan deserts and eastward to the Hindu Kush mountains in Afghanistan
~ Extended to Kabul, Ghazni and Kandahar ; also Pakistan Indus valley

By Dr. Israr Ahmed & Sheikh Imran Hosein : Khorasan (i.e. area which now includes Afghanistan, NW Pakistan (Malakand Devision) , NE Iran, Central
Asia in north of Afghanistan etc.).

By Mir Ghulam Mohammad (Afghan historian) : Balkh (in the East), Merv (in the North), Sistan (in the South), Nishapur (in the West) and Herat, known as The Pearl of Khorasan, in the center. While Improper Khorasan's boundaries extended to Kabul and Ghazni in the East, Sistan and Zabulistan in the South, Transoxiana and Khwarezm in the North and Damaghan and Gurgan in the West.

References :
~ Scholars :
~ Greater Khorasan :
~ Maps & their boundaries with history :,_Iran,_Pakistan
etc etc etc