Dealing with proofread wikisource book, I think that Index pages could be exported too with a specific tool, saving original pagination of the edition (t.i. converting individual nsPage pages into individual pdf pages).
The result could be, more or less, the same that can be viewed by it.source "viewer":
Don Chisciotte
I presume that conversion could be much simpler than the conversion of ns0 pages, and that it turned out as a much more faithful digitalization of source edition, while ns0 transcription is something like a "new edition".