Have had a closer look at the Royal Library in Zephyr Heights. The books are divided by inexplicable symbols on the book spines, but all the books that were pulled out by Zipp and Misty, with the exception of the book about the alicorns, have a small symbol in the middle of the cover.
This symbol appeared to be Twilight Sparkle’s symbol, a star with eight or more prongs seen from the last episode of S9. This symbol was also seen in the special C3. Twilight did not use her “pure” cutie mark as her trademark during her reign, but a symbol with eight visible prongs - her cutie mark has six purple prongs and six white prongs, at longer range only the middle white prongs are visible. This symbol on the covers appeared to be Twilight’s.
This could be proof that the library was once Twilight’s, and that those who took over ZH after Equestria’s collapse kept this tradition alive around newer books and ceremonies, with the Wishentine being the example. The book about the alicorns also appeared to be handwritten and was likely just a single example, possibly written by Twilight herself as a personal project. This book does not have Twilight’s symbol on the cover, where Celestia and Canterlot could be seen. The book may have been created in the time after Opaline was defeated several centuries ago.
The library housed an enormous amount of knowledge that the pegasi royal family could have used for their own purposes, but that did not seem to have happened. Still, it means that Queen Haven and her predecessors may have the only original library from the time before Equestria’s collapse, and the small symbols on the covers may have revealed this.