Extensions have never been guaranteed, that's why you've always had to apply for them. Admittedly they're rarely refused but they're not a given and never have been.
You need to prove the 800k was in your bank account for 3 months after you received your extension and didn't drop below 400k for the whole year of your extension in order to get your new yearly extension based on 65k per month
Immigration will see your previous years extention and would almost certainly want confirmation that you followed the financial requirements of that extention