In your first post, you say "There are also 'longitudinal' themes that are studied in all three years, and which are relevant to every placement. Examples might be ‘Ethics and Law’ and ‘Leadership and Management’."
I would say that (for instance) Ethics and Law informs Leadership and Management, and you say yourself that these longitudinal topics are relevant (underpinning) to every placement.
It seems sensible to show your students how themes link, and to do so as simply as possible from both the admin, the teacher and the student point of view. So I would suggest putting them into one course. You can, of course, put them into different sections (topics) within one course (when I say 'course' I mean it from the Moodle point of view)
I think this is the advice we are all giving you - to think about the curriculum you are teaching in a more unified and joined-up way.