Limitation period clarified: refund claims and document amendments measured from payment of duty or interest. The amendment renames the existing Explanation in section 27(1) as Explanation 1 and adds Explanation 2 clarifying that the one year limitation period for a refund claim under clause (b) of sub section (3) of section 18A or for amendment of documents under section 149 is computed from the date of payment of the relevant duty or interest.