Year of the Notional Serpent
This is the year in which the events of the book Small Gods took place. It fell in the Century of the Fruitbat and in context might be between fourteen and twenty years after the Year of the Astounded Beetle, when Brutha was two or three and got his first inkling of a wider world outside Omnia, when he saw an Ephebean coin.
The text, on page 72 of the Corgi paperback, notes that in his own perfectly eidetic memory, Brutha was "one month shy of three years old" when this happened. Vorbis in the present then assesses him as being seventeen or eighteen years old. Therefore the intervening gap between the two named years is, in all probability, no less than fourteen and no more than fifteen years. Brutha adds the incidental detail that this event was on the 3rd Grune. If there was only one month to go before his third birthday, Brutha's birth month would be the one that follows Grune in the Discworld calendar. (Gruly?)