Case: 7 orphaned sitemap files, reconnected

Case: 7 orphaned sitemap files, reconnected
A migration left 7 sitemap files live on disk but absent from the index. ~40,000 URLs were never discovered.
What we did:
— Crawled /sitemap_index.xml and listed referenced children
— Diffed against files actually served under /sitemaps/
— Found 7 unreferenced files, added them to the index
Measured outcome over 5 weeks:
— Newly discovered URLs: ~40,000
— Indexed pages rose 9%
Audit to run monthly:
✅ List every sitemap file served by the app
✅ List every child URL in the index
✅ Both sets must match exactly
Definition of done: zero files on disk are missing from the index, and zero index entries 404.