If they use letters instead of numbers, note that letter "A" is the first alphabet, not zeroth alphabet.
Definitions are fine, and I agree that "A" is the first letter. But that's no use to people who need to think clearly about the offset between "A" and "C" right now. Should I tell them they're wrong, they have to count to three and then subtract one? Because the dictionary says so?
Book chapters and page numbers are not offsets.
> Book chapters and page numbers are not offsets.
I don't know but I feel like you are making a point out of something arbitrary. When I listen to an audio book, everyone always says: "Chapter 1", not "the first chapter" so why is this important?
I think extreme attention to to arbitrary meaningless details is how we ended up with most rules in language that we are starting to collectively detest.