Missing sales fy 2018-19 gstr 9a

A trader operating under the composition scheme, dealing with both taxable and exempt goods, inadvertently omitted exempt sales like rice and pulses from their GSTR quarterly returns for FY 2018-19. The query seeks clarification on whether tax is payable on these missed exempt sales when declared in the annual return (GSTR 9A), and if so, what penalties apply. The user is also requesting specific notifications or rules pertaining to this situation for composition schemes.