Extension of GST tax exemption under section 9(4) postpones the chargeability date and applies retrospectively. The Governor, under section 11(1) of the Assam GST Act, amends Notification No. FTX.56/2017/21 as amended to substitute the earlier cutoff date with the 30th day of June, 2018, thereby extending the exemption from payment of tax under section 9(4); the amendment is deemed issued on the 23rd of March, 2018.