Reporting to Pattaya Immigration to show you still have 800k in bank for 3 months from getting extension renewal doesn't matter if it is after the date they gave you as it will still show you kept funds in bank for the required period. In the past, reports from folks that planned to be out of country or out of Pattaya on the due date they were given asked Jomtien Immigration about it and were told no problem, just report when you get back.
That said, from reports I have seen, Jomtien Immigration has no system to track such reporting and when you do, they do not enter any information to show the report was made. So one could skip reporting entirely without any problems -- but, still probably best to make the report to be on the safe side.