In Dirk Gently's Holistic Detective Agency, the alien ghost that seeks to supplant all life on earth is thwarted when Dirk Gently, in the guise of a man from Porlock, distracts Samuel Taylor Coleridge from writing the "second and far more disturbing" section his poem Xanadu, and by provoking him to change The Rime of the Ancient Mariner so that it involves an albatross, rather than an asteroid.

Changing these poems suffices to make it impossible for the alien to complete his mission. It is implied that the alien had stored certain information in the poems that he himself would need later to save his spacecraft, four billion years in the past.

Why? What information could possibly have been encoded in the poems that the alien ghost did not already know (since he was the one doing the encoding in the first place)?