If your source map is scaled up, the filled map and empty map count become somewhat unintuitive.
In my example, I'm using a 1:8 scale atlas with 43 filled maps and 354 empty maps remaining, but it has stopped filling new area.
354 / 43 = 8.2 meaning technically, the atlas has used all available empty stock as its "using" 8 empty maps per map added to the atlas.

I recommend having the displayed empty maps be converted to filled in the tooltip based on the source map scale, meaning your empty stock should be chunked by 8 for every new map loaded in 1:8 scale.

so im not sure i get this correctly. what does scale have to do with it? scale is just a property of maps. One could consider it a bit cheary but the atlas will just consume 1 map regardless of the scale so even at high scale to create a new map it will consume a n empty map