Yes, however if the AI cheats then players often feel rather wrong done for by the developers and they get complaints ect. If it was to be implemented it would probably be an option in the game menu whether to have on or not to have it on, some players may not like it. As I have said, some players often prefer to have a large array of units rather than one unit that upgrades.
However there is a way to get round this. Hastatii, Principles and Trarii could be trainable at the start, but if unit of Hastatii gets to three chevrons then it becomes a unit of Principles, which then, under the same circumstances, could become a unit of Trarii.
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