There is a large variety of civilizations for random to choose from and that doesn't mean that the same civilization could be chosen more than once in a row. The way these things are going, it could be possible that there will be more civilizations in the future and that these civilizations will also get chosen more than once in a row. Just because there are many civilizations, it doesn't mean that there isn't a possibility that the same civilizations can be chosen. For example, I've had Wu Zetian chosen for me on random in my last 5 games. I've also had Ahmad Al Mansur and Bismarck chosen as ai civilizations in my last 5 games, approximately.