Upstream cache age
Also: cdn cache age
How long ago a response was cached by a CDN in front of the target site, which is added to a scraper's own cache age to give the real age of a row.
A freshness field that counts only the scraper's cache reports the age of the request rather than the age of the data, which can differ by a day on a page behind an aggressive cache. Forcing a fresh fetch makes the scraper re-ask; it cannot make the CDN revalidate.