If you tell lilypond-book (using --include=lilypond) to look in the
lilypond directory for the file ../config.ly, it can't find this file
because it doesn't exist (because of .. you end up in the parent directory).
It might be sufficient to specify only one subdirectory e.g.
--include=lilypond/tuneA (and not all subdirectories one-by-one) since
then it can find the file at lilypond/tuneA/../config.ly
Makes sense?
Cheers,
Julien
Yes, it does make sense, thank you very much for all your precisions. I’m going to sharpen the file organisation of my project.