I just recently realized that the parts of a book aren't "forward" and "afterward", but "forewords" and "afterwords". Like the words before the main content and the words after the main content. Ugh. That sounds like a definition. Which, I guess, it is. But what I'm getting at is that they're about the words, not direction (Cf. "homeward", "westward"). They're just transparent compound words, but their coincidental similarity to some other words obscured that fact. Language, y'all. It's weird.
@benhamill Some random wiki searching, in order:
https://en.wikipedia.org/wiki/Foreword
https://en.wikipedia.org/wiki/Preface (via searching for "praefatio")
https://en.wikipedia.org/wiki/Dispositio#Exordium
I was guessing biblical in origin, but this makes sense as well