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.