ISO instant the sweep ran; ka sources show can say how stale the map is.
The ranges actually read, so a later run knows what is already covered.
A list rather than one from/to pair: merging two disjoint sweeps (7900–8000 and 9000–9100) into a single span would claim the 999 numbers between them had been read. A later run would then skip them and the map would look complete while being silently full of holes — the failure this project is built to avoid.
Question Drucksachennummer -> the answer that names it.