Look at even older writing and you'll see em-dashes there too: Edgar Allan Poe, Lucy Maud Montgomery, the Brontës, among others.

> “No, reprobate! you are a castaway—be off, or I’ll hurt you seriously! I’ll have you all modelled in wax and clay! and the first who passes the limits I fix shall—I’ll not say what he shall be done to—but, you’ll see! Go, I’m looking at you!”

-- Wuthering Heights (1847), Chapter 2, Emily Brontë.

I wonder what the frequency of AI common words like delve and other words/phrases are in Project Gutenberg, Wikipedia, and other collections.