Each subheading of the refund nomenclature shall be provided with a numeric code of eleven consecutive digits as follows: (a) the first eight digits shall be those of the numeric code for the relevant combined nomenclature subheading; (b) the ninth, 10th and 11th digits shall identify the refund nomenclature subheading. If a combined nomenclature subheading is not further subdivided in the refund nomenclature the last three figures shall be '000'.