I was under the impression that the 800k baht is left in your account for 1 year and not added up the following year, the following year it can be 400k baht but not to go below that.
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.