If you look at the fine print, it says "any flight or connecting flights," which would mean to me that UA allowed for this type of use of the certs when it issued them. It may be true in Oz (this was the case in MEL, as well as at IAD, which although not in Australia often feels like a different planet altogether) that the personnel don't know this feature of the certs; but elsewhere they certainly do, and cheerfully honor the provisions of all certs, which is more than some of the users do.