Well, we also had the telephone – and memos, sometimes delivered by a mailman and sometimes by an office courier and sometimes, gasp, in person by the boss himself. Or maybe just his secretary.
But when I began drafting Big Inca Versus a New Pony Express Rider, the Internet was somewhere over the horizon. Yes, online communications did exist in what we now consider some crude form. That’s progress for you, I suppose.
Still, in developing the story, I wanted some kind of encrypted exchange between the distant handler and young Bill in the field, and that led to the technical arrangement described in the novel.
Thus the events could be disclosed in a series of memos covering a three-year period. It’s almost like playing cards, one at a time.
To tap into their exchange, just click here.
Jnana's Red Barn 
some of the text i get from my children still look like teletype – this made me smile 🙂