Definition of appropriate duty broadened to include nil and concessional rates under amended excise notification. The notification substitutes the reference to section 66 with section 66B in the opening proviso of the principal Central Excise notification and inserts an Explanation that appropriate duty, appropriate additional duty or appropriate service tax includes nil duty or nil service tax and concessional duty or concessional service tax, whether or not read with any relevant exemption notification for the time being in force.