Mistake: trusting your own lastmod when the data hasn't changed

Mistake: trusting your own lastmod when the data hasn't changed

A nightly rebuild stamps every page with today's date in lastmod even though the underlying row is untouched. Google learns your lastmod lies, stops trusting it, and slows recrawl of the pages that actually did change.

Lastmod integrity SOP:
— Step 1. Owner: dev. lastmod is computed from the data row's real updated_at (max of the fields rendered on the page), not from build time.
— Step 2. Owner: data. Track a content hash per page; bump updated_at only when the rendered hash changes.
— Step 3. Owner: SEO. Sample 100 pages, compare sitemap lastmod against the last real data change. Gate: dates match within 1 day.
— Step 4. Owner: SEO. Confirm in GSC that recrawl frequency tracks actual change rate, not build cadence.

Guardrail: lastmod reflects content change, never the cron schedule.

Ship gate: don't publish until all boxes are checked.