The Epilogues of Tsun Dng is a strange book, even when compared to the other books of the Mythos.
It is a multiple volume set, with an indeterminable number of volumes. You see, like the branches of time itself, the copy of Volume 1 that you have may lead to any of a number of Volume 2's, any of which could lead to any of the Volume 3's. Also, as is inherent in the nature of Yah'kwi'aa, the past is branched as well, so a particular Volume 2 has many potential Volume 1's.
The Volumes can only be reliably read in the Dreamlands. The unstable nature of the work makes it impossible to exist in the physical world. So, studying it in the Dreamlands can give spells, Cthulhu Mythos and Dream Lore, but memories of what you read, like a dream, often lack detail. It is also difficult to dream yourself back to the exact book and passage every time you sleep.
A Waking World version of the epilogues exists, but it contains no useful information. As it is the dream of a Dreamlands book, it appears as a mouldering old tome, but it only describes people and events in the area around the book, but in a difficult to read, arcane style. THis will tend to create paranoia in the reader, as he believes that this was written long ago, but it is really just a textual mirror of the reality around the book. The Waking world version does have a practical use, though. Time spent with this version increases the chance that you can return in the Dreamlands to the specific volume and chapter that you wish. Acolytes in the Gang of Time spend much time in the pointless task of deciphering the Waking World version, so that when they sleep, they can continue their real studies of Time.
Reading this tome can grant a wildly dangerous skill called Timesculpting. Strange events surround the reading of either the Waking or Dream editions: deja vu; flashes of insight of everyday events, like traffic jams or quick lines at the grocer; or odd fugue-like events as things get caught in eddies of time, such as the same spider walking across your desk all day, or a CD will repeat the same track endlessly, or a burp will remind you of the food you ate at some point, but it happens at the same time, every day.
There is no indication that anyone named Tsun Dng, or any of the likely transliterations of this name, have ever existed. Neither learned inhuman socereror nor even Randolph Carter have never been able to find any reference of this ancient wizard. It is possible that he did exist, and now does not, anywhere in time. It is the nature of time itself (or is it the nature of Yog-Sothoth, or the nature of Yah'kwi'aa?) to thwart manipulation, by eliminating the existence of the irritation. This may have been what happened to Tsun Dng.