When you ask Prometheus for metrics from a particular timestamp in general nothing will actually exist as that precise time. Scrapes happen periodically and the time isn’t known until it happens. So Prometheus actually looks for the most recent scrape value before the timestamp requested. By default it won’t look backwards forever and instead will only look back by a maximum of 5 minutes. As a result if a metric stops being collected it could still appear on graphs for a short period of time.