I have been trying the past few hours to create "Unique" buildings.
However i do not want them buildable from the start.
Specifically: I mean to give the player the tech "Diocletean's reforms" in 284AD(through an event).
This tech will allow the production of new field legion units AND fabricaes(factories).
At first i made Diocletean's reforms as the sole prerequisite of fabricaes, which in turn had two Nos as prerequisite.
It did not work.Fabricaes kept having "No" as a prerequisite and did not appear in the production list.
I then tried giving the "Diocletean's reforms" tech a prerequisite of its own f.e "Triumvirate". It too had as prerequisite two "Nos".
At first it seemed it worked. Fabricaes appeared having as a prerequite "Diocletean's reforms" and could be build normally upon the acquisition of the tech. That was only an impression however as the next time i loaded the game everything was reset and fabricaes had No as a prerequisite.
As you already experienced, "Diocletean's reforms" needs a preq of a no,no tech and nil to work. It doesn't matter if the second preq is nil or another normal tech on the tech tree.
It can't be a no,no tech itself, because while they can be given by events, they cannot enable structures.
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The Slim End Of The Long Tail - Kaplak Stream