Thanks for your replies and links to other threads which I hadn’t seen.
I think at the end of the day including album pre-release single track downloads or streaming previews under the release group for the relative album might be the best idea. <My opinion!> That way at least we get an idea of the ‘history’ of the release itself, ie. seeing that a certian track or tracks were released prior to the full release.
This would be the case if the track is not to be considered a ‘single’. We are obviously talking about digital download/streaming tracks only here of course.