I know what you are getting at, but there is an example in the cf spec (may not be intentional) that has different dimension names for the points and bounds vars. The way I've coded it means that provided the shapes match and the vertex dim is last this helper function will not be called so we are not enforcing it in a wider sense. If the shapes don't match this will be called and I've assumed they match in order to associate them, hence the note.