How do you decide a listing is actually dead when nobody tells you?

Nobody tells a job board that a position was filled, so all we can watch is the source. Our rule right now: if a source was fetched in full and an id is no longer in it, that listing gets archived, and if the fetch was partial we close nothing. There are holes on both sides. Some sources keep old posts up for months, so anything past 120 days only lands on a suspect list, because we don't trust age alone enough to close it. And one source handed us its error page instead of a job, so "Sorry, we couldn't find anything here" went live as a title until Search Console flagged it as a soft 404. If you run a directory or marketplace built on other people's data, what finally convinced you something was gone: the source, your own checks, or users reporting it?