What Only a Scheduled Crawl Reveals
A single export tells you what SimplyHired displayed on one afternoon. The signals worth paying for appear when the same searches are walked again on a schedule.
Freshness has to be measured rather than read. The only sitemap declared in robots.txt is the viewjob sitemap index, and its child sitemaps carry a location element and nothing else - no lastmod, no changefreq, no priority. Nothing in those files says when a listing appeared or last changed, so first-seen and last-seen dates exist only if someone crawled and compared.
Disappearance carries meaning. When a job key stops resolving, or drops out of the searches that used to return it, the role was filled, paused or expired. The span between first-seen and last-seen is the closest available proxy for time to fill, and it is only available to whoever was watching.
Reposts are the other half of the picture. Employers relist the same vacancy and SimplyHired issues a fresh key, so the URL alone will never tell you it is the same job. We match on employer, title, location and description body to link repost chains, and keep both the original key and the chain identifier so you can count either way.
Salary edits, changes of job type, and the rotation of Sponsored placements all show up as diffs between runs. Every delivery can carry the full snapshot plus a change file of new, updated and vanished keys.