I have before pondered the Codex of Ultimate Wisdom and it's nature according to the lore of Ultima. I have earlier held the point of view, that the Codex at all times could only be read by those on a sacred quest and thus that it was impossible, that Blackthorn could ever have read it in u9 even if he had had the lenses.
Yet, after a more detailed investigations of the gargoyles' history I have come to see that I was wrong. The Codex itself could indeed in the beginning be read by anyone. Yet, the Gargoyles enshrined it within the temple of singularity and this temple prevented anyone from entering except those on a sacred quest (which the Stranger undertook as he became the Avatar).
The humans of Britannia later enshrined the Codex in a temple on the isle of the Avatar and this temple also blocked anyone from entering, unless they were on a sacred quest. Thus it were the two temples and not the Codex itself, which made it necessary to be on a sacred quest in order to approach it. The proof of this is, that as the Codex was placed in the Ethereal Void during the third age of Enlightenment, only the lenses were needed in order to read the Codex and not a sacred quest. Both lenses that is. One lense alone would not work.
After the passing of the third age of Enlightenment we do not hear very much about the Codex again before the third age of armageddon (u9) where Samhayne, a pirate, hath gotten his hands on it somehow. During the 200 years the Avatar was away from Britannia, first on Serpent's Isle and later in Pagan, the Codex was removed from the Ethereal Void by means unknown. Even though the Codex is no longer in the Ethereal Void the two lenses are still needed in order to read the Codex. The reason for this must be, that the Codex has become heavily affected by it's return to the Ethereal Void and thus it has become "Ethereal Voided" meaning, that even through it has left the Ethereal Void it acts and reacts, as if it was still physically placed in there. Indeed a matter, which it is hard to fully understand, but nevertheless it is the case.
I have earlier held that the Codex was to be thought of as a kind of entity rather than just a book, and that point of view I hold still. It seems to me that it was on purpose that the Gargoyles found not the eight Virtues of infinity, but the eight Virtues of singularity when they read the Codex. There are more solutions as to why the Gargoyles and Humans found different systems of Virtue (Infinity vs. Singularity) in the Codex, but one explanation is that the Codex showed them different things on purpose and that is the explanation I am inclined to deem correct.
I am aware however that in the end it is a guess.