Cleaning progress opens more of the map
That relationship comes directly from the official description. The safest practical method is to watch the boundary and the progress display together.
Record what is reachable
Before the next sweep, note every visible boundary and landmark you can enter.
Clean and compare
Clear reachable ground, then compare both the visible progress and any boundary change.
Name it privately
If access changes, describe the landmark in your own notes. Do not treat that label as an official area name.