Thanks for sharing with me about --delete-before. In my subsequent investigation into it's use I found the manpage says that using that option disables 'incremental recursion'. What is 'incremental recurssion'? I assume that I will still be able to backup lower level directories.
Some options require rsync to know the full file list, so these
options disable the incremental recursion mode. These include:
--delete-before, --delete-after, --prune-empty-dirs, and
--delay-updates. Because of this, the default delete mode when
you specify --delete is now --delete-during when both ends of
the connection are at least 3.0.0 (use --del or --delete-during
to request this improved deletion mode explicitly). See also
the --delete-delay option that is a better choice than using
--delete-after.