Haven Kimmel question…

We’re listening to Haven Kimmel’s The Used World and something about it is driving us nuts…

There are “letters” at the beginning of chapters and even in the middle of chapters. WTF are those?

At first, I thought the letter referred to a memory or an experience one of the characters was having “H” for “Hazel” or “C” for “Claudia” but that doesn’t fit because what the heck is the “P” about? And there’s no “R” for “Rebekkah” as far as I have heard.

TW is thinking the letters are related to the “address book” that is in Hazel’s room in the Emporium but still, that isn’t making sense.

Who has the print copy in hand? Did we miss something that clarifies what the heck these letters are about?