Chapter numbering explanation in Three Rooms by Jo Hamya

I’m a new fan of millennial fiction and Three Rooms is next on the list! This is a super specific question and I really hope it gets to the right person because I googled around and couldn’t find an answer.

What is the chapter numbering about? Divided into three parts it goes:

Part I I.VI, I.V.I, I.V.II

Part II II.III, II.II, II.I

Part III III.N

What is this?! I always like to ground myself before starting a book by seeing how it’s organized and this has thrown me off.