You set `populated` after you've re-indexed: https://github.com/mozilla/kuma/pull/2167/files#diff-39103a413f8b71eaa71f363c6a323addR33

So that conditional wouldn't work because if a document change happened while you were re-indexing it would only update the current index and not get flagged as a document that needs to be updated in the successor. Then when you switched indexes you'd lose the most recent document.