I believe I do have a timeline of events that you might find enlightening.
Spencer explains that the SOE communicates with field agents using “poem codes”. The message sender and recipient encrypt their messages based on an agreed upon passage of text. For security, this text must be carried in the agent’s head, but not be something well known generally.
The passages need to be intensely memorable, unpredictable and, ideally, consist of twenty-six words.
Spencer recalled the rhymes that Newt used to teach him in class as memory aids, and thought that Newt could help with this. He tells him that suitable passages were in great demand.