As per section 11(3) of CGST Act e Government may insert an explanation in any notification issued under section 11, for the purpose of clarifying its scope or applicability, at any time within one year of issue of the notification.
The explanation was inserted within one year of the insertion of the original entry prescribing concessional rate, so that it would have effect from the date of inception of the entry i.e. 21.09.2017
However, like other notifications issued on 26.07.2018 to give effect to other recommendations of the GST Council, the said notification also contained a line in the last paragraph that the notification shall come into effect from 27.07.2018.
It is therefore clarified that the explanation having been inserted under section 11(3) of the CGST Act, is effective from the inception of the entry.