What Aetius has said doesn't apply to the patch in my experience. The AI makes himself nummerous protectorates: Im now a few decades in a Parthian campaign and the Gauls have Germany as protectorate and the Macedonians have Thrace... Germany is at its starting provinces, while Thrace holds its home and Byzantium, wich I presume was returned by the Macedonians when Thrace became a protectorate.