It works fine from Finale.
Maybe my Finale is too old – 2010 … Funny clef placement, by the way!
Indeed, but I can’t imagine you’d hang onto that treble clef anyway.
Just tried again today.
Importing a modified music.xml into an existing Dorico project does not work.
But opening a (modified) music.xml file with Dorico will import it with the right number of staff lines.
Yes, you’re right: it will only work as a new document. Sorry.