Correspondence Books
You can combine them? I was not aware.
They become one book once you’ve collected them all, I believe. I have one book in my inventory, anyway.
Cool. I’ve not yet collected all the pages/letters.
Wait! Now that I think about it, I haven’t received any letters as items. Just the ‘book’, which I put in the bank.
Hmm, I don’t know what will happen when I find another letter.
You get another book. There is no need to keep the book for the letters though you probably want to until you are done. Every time you interact with a letter you get a new book if you don’t already have one.