11 August 2020
In case GST credit for the period FY 17-18 was not taken in books or GSTR-3B or Annual return (nor shown as ITC on inward supplies received during 2017-18 but availed during April to September, 2018) and the same is taken in FY 18-19 but expense pertaining to the same is considered in FY 17-18. For Eg: FY 17-18: Exp. A/c Dr. 118 (Including GST of Rs.18) To Party A/c Cr. 118 FY 18-19 (Sept 18): GST A/c Dr. 18 To Exp. A/c Cr. 18
13 August 2020
You can show it under current year ITC in 2018-19 annual return. Legally the availment of ITC is correct . However,there is wrong reporting in the 2017-18 return.At the most there can be some penalty -depends on the amount involved as well.