GSTR 1

You can. ensure that you have paid taxes through GSTR-3B. If not paid the tax has to be paid along with interest. (if ithe missedout invoices are outwad supply invoices).

Considering the such details in subsequent financial year may lead to reconciliation issues at the time of annual return filing.

If you can't upload the details in GSTR-1 of subsequent error, pay tax through GSTR-3B to avoid interest liability. 

you can disclose missedout outward supply details even under annual return (due date 31st Dec). But your customer will not be able to see such details in this GSTR-2A which may creat some issues for him. 

try to enter the details directly in the portal and check if it is accepting. 

offline tool has some issues like this. Hence, the same has to be added directly in the online.