Any stamp duties levied and collected in the Union territory of Manipur during the period commencing on the 16th day of April, 1950, and ending on the date on which the Indian Stamp Act, 1899 (2 of 1899), as in force in the State of Assam is extended to that Union territory under section 5, in the belief that the Indian Stamp Act, 1899 , as in force in the State of Assam immediately before the 16th day of April, 1950, was applicable to that Union territory, shall be deemed always to have been levied and collected in accordance with law.