show- cause notice limitaion for 2017-18 18-19 - Goods and Services Tax - GST

respected sir, department is issuing intimation letters to taxable persons relates to FY 2017-18 ,2018-19 in respect of differences between GSTR-1 data and GSTR-3B data and asking for explanation. and notices are giving under SEC-74 . my doubt is whether , issues relates to differences between GSTR-1 and GSTR-3B covered under sec-74 notices or not . please guide me thanking you