Every Publisher is KING. They do it THEIR WAY (AKA 'House styles').
You need to reverse engineer every book.
And just because a House has Rules (The House stylesheet), does not mean the person (lowest bidder?) used it correctly
I have seen a whole book mostly coded
class="frontmatter" 
because that was the first CSS entry that
looked OK to the coder.
A House stylesheet may have a dozen styles that are currently the same. The Theory is, 'I can change the look of any page
type later.'