Hi Peter, > Oh dear, it didn't! The staff in question (in my score) isn't at the top of > the full score. It's a piano 4-hands score so I want the Ritard. to be at the > top of staves 1 & 3, but not 2 or 4. To the tweak in the snippets won't work > either as that puts marks over all staves.
You need to look into MarkLine (also known as ScoreMarks) — a custom context that includes only rehearsal marks, tempo markings, etc., which is then included at only certain points of a multi-staff score. Cheers, Kieren.