Section 4(2)(b) in The Punjab General Sales Tax (Amendment and Validation) Act, 1987
(b)where such supply, not being any such supply by any restaurant or eating house (by whatever name called), has been made at any time on or after the 4th day of January, 1972, and before such commencement and the aforesaid tax has not been collected on such supply on the ground that no such tax could have been levied or collected at that time: