Trying to have two different types of factories, each independent of the other
I have created a "city" unit, which can only produce infantry, militia, and marines and then a "factory" unit, which can produce only other types of units. Each has multiple levels, but at the lowest level each is limited to producing three units. However, when a territory has both a city1 and a factory1, instead of being able to produce up to 3 infantry units plus up to 3 other units, only 3 units overall can be made.
Also, the requireUnits limits are related to the territories, not to the units (you need having that unit in that territory; you don't need that unit being the one that it is producing it); so, even if they would stack (which they don't), you would be able to produce the union of all units allowed by any (thus whatever up to the total limit, if the factory allows whatever).
So, what you want to do is twice unsupported (yet, you can obtain it via massive triggering and produce / consume units).