GUYS GUYS GUUUUUUUUUUUUUUUUUYS
The book isn't official canon, its fictional also the whole "appearing in glaciers" was a nord legend which isn't surprising because nords always expand on the truth or just like to believe in fantasy like how they think blizzards and missing children are the fault of falmer spirits, that skyrim was their true ancestral home even before they did their genocide on the snow elves, all elves are evil and trying to kill off the human races and various other lies and fantasies. Nord legends shouldn't really be taken with even a grain of salt.
Prove it, A Cyrodiilic Vamp would not write down accurate information of his secretive order for the living to find. Provide one shred of evidence the author isn't a lying Volkihar. Or maybe its all a pack of lies by Movarth Piquine just to make himself famous.
I don't trust the word of a vampire especially when in the form of advice about vampires
The other clans don't like each other, hell the Morrowind vampire clans are constantly at war with each other also theres no evidence that this book has any truth too it and if you say "well Movarth is in skyrim" then you are still wrong because we don't even know if its the same person especially since Movarth doesn't have his last name and the fact that there are no references to the book nor does he confirm it in-game.