Where does <$chaptertitlename> get updated?

Speculatively, though FM and I have had a reasonable working understanding of each other's ways for a while now, I'd guess that a chapter is a single .fm file. I've never used <$chaptertitlename>, and would have conceptual problems trying to imagine what the name of a title would be in the first place :-}

[short pause for indepth research]

• from one test, it looks as though <$chaptertitlename> pulls in the same info as <$filename> – as such, it would only be updated by changing the name of the file
• for a second test, I went a bit farther and set up a folder containing three .fm files … my vague hope/expectation was that using <$chaptertitlename> in one of the .fm files would then pull in the title of the containing folder

No such luck, even after updating the book. I didn't bother trying to find out whether the $section variables pulled in content from the second and later files in the folder.

So I conclude I don't have any understanding of this variable and its $section relatives.

Try:

FM9 Hierarchical Books: New variable

and

<$chaptertitlename> gives unexpected results