[11] The Koch people in this group are those who have preserved their languages, their animistic religions and follow non-Hindu customs and traditions.

[15] The Koch people consist of nine ethno-linguistic groups: Tintekiya, Wanang, Koch-Rabha/Kocha, Harigaya, Margan, Chapra, Satpari, Sankar and Banai.

This is diagrammatically represented as — Koch-Rabha (Kocha)→ Wanang→ Harigaya→ Margan→ Chapra→ Tintekiya, where the adjacent dialects exhibit more lexical similarity than those at the ends.

[23] In Takabat-i-Nasiri, which contain records of Muhammad bin Bakhtiyar Khalji expedition into Kamrup in 1205 A.D, mention that the people inhabiting between the country of Lakhanawati (Gauda) and Tibet were the Kunch (Koch), Mej/Meg (Mech) and Tiharu (Taru).

[24][25] In Persian history, these population (Koch, Mech, Tharu) possessed the physiognomy of the Turks and the Mongols and their language was different from the rest of the subcontinent.