ANSWER: First, for the sake of correctness, the Governing Body of the Watchtower Society is a relatively recent institution, being set up in the early 1970’s. But, to be sure, the original Bible Students surmised that C.T. Russell was the faithful and discreet slave and ever since then there have been various iterations of the slave class.
As for the series of parables Jesus spoke all of them have a common theme; namely, that Jesus is the master and in his absence he appoints or entrusts his slaves with certain responsibilities. (The responsibility of the 10 virgins is to be ready.) And, indeed, it is understood by the slaves that upon the master’s return they will be called to make an account of themselves to him.
It was Jesus’ style to teach by telling short, easily-remembered stories, like the prodigal son or the rich man and Lazarus or the story of the so-called good Samaritan. Each story has a powerful lesson. The stories of the faithful slave and the evil slaves encourage towards faithfulness, accountability and watchfulness, to be sure, but they only have relevance due to the fact that Jesus is coming to call all to judgment.
So, while the parables in question are not really prophecies in themselves, they are based upon the fact that Jesus is coming as the judge of the house of God. And virtually all of prophecy bears witness to Jesus, either in his role as the ransomer or as the appointed god and judge to whom all will render an account.