What changed in the universe, and when.

A book is deterministic for a given universe, not for all time. Move one conviction score and every book touching that theme reweights. So the universe is versioned, every book URL records the version it was built against, and a book built on an older one says so instead of quietly showing you something else.

Older books are flagged, not preserved. Rebuilding a book against the universe it was written on would mean keeping every past version, and that is not built — which is why the notice says the holdings may have moved rather than claiming to restore them.

26 themes are published in full on the universe page.