Think about this: is there any point in If on a winter's night a traveler when you, the character, are totally and completely sure that the book you're reading is, well, the book you're reading? And doesn't that kind of mess with you, the human Shmooper?
The trickster-translator Ermes Marana has counterfeited and mistranslated text to the point where titles are constantly confused, books with completely different storylines are posing as the same text, and there's actually an international literature conspiracy based completely on lies. Ultimately, Calvino brings into question the authenticity of any text you read, which is kind of concerning to us Shmoopers.
Ultimately, Ermes Marana is the true hero of If on a winter's night a traveler.
In the conflict between two sects of The Organization of Apocryphal Power, Calvino is on the side of The Archangel of Light, the group that believes it can encounter absolute truth if it finds the right book.