duly stamped "duly stamped", as applied to an instrument, means that the instrument bears an adhesive or impressed stamp of not less than the proper amount or the amount of initial duty or the amount of advance duty paid under subsection 37(1) and that such stamp has been affixed or used in accordance with the law for the time being in force: Provided that a stamp certificate or official receipt for the proper amount or amount of initial duty or amount of advance duty may be attached or affixed to any instrument in lieu of the stamp, and the instrument shall be deemed to be duly stamped; ACT 378 - STAMP ACT 1949 (CONSOLIDATED AND REVISED 1989) 2. Interpretation.