Accurate as in theories.
The documents mentioned are just that, things that may have been, you think the bible has not stirred shit up in it's existence? Still some people take it to be true from word to word, others think Jesus existed.. eventhough as a mere mortal philosopher.
You find a scroll, an interresting writing of a sort, which is surrounded by the world's largest religion, and you have enough to write 50 book's in which you can state "all descriptions of artwork, architecture, documents and secret rituals in this novel are accurate". As long as you follow the guidelines, and dont go spewing off shit that does not appear in the original text, however flawed it might be, you're home free.
Therefor that dramatic "all descriptions of artwork, architecture, documents and secret rituals in this novel are accurate" line can be said with a clear consciousness.