Please clarify the ITC (HS) of yarn made from worn clothing, the material composition of which varies from lot to lot. It is uncertain as the clothing may be of cotton/woollen/ man made fibre?

Under HSN, the classification of yarn is on predominance basis. So the yarn having predominance of wool would fall under Chapter 51. If all kinds are in equal proportion i.e. no fibre is predominant, it will get classified in the chapter covering the fibre last in the numerical order, so Chapter 54 or 55 in case MMF are present.