In the book its relevant also that there is a suspected mole (double agent) and the protagonist knows it is one of 4 people, hence 3 innocuous titles and 1 spy.

In the book its relevant also that there is a suspected mole (double agent) and the protagonist knows it is one of 4 people, hence 3 innocuous titles and 1 spy. (After all the rhyme goes on with plenty of other epithets)