There’s also the tag darktable|changed:
The history filter shows:
I exported one of the images:
So, it is now unchanged since the last export; exported increased to 7, changed decreased to 30.
history still shows:
I now changed that same image in the darkroom:
darktable tags:
exported remained at 7; changed is back at 31.
history still shows:
Then, I discarded the history stack of the image.
darktable tags:
It remains exported, but is not considered changed.
history filter:
It’s no longer altered, is registered as auto applied; basic remains unchanged.
(Later I found sometimes history did not seem to update; I may check this later and raise an issue if needed, but since I don’t really use those filters, it’s not a priority to me.)