That was what I thought, but I had to check it which I already had done. Here it is:
thieves_guild =
{
lasting_effects =
{
percentage_score = { gold = 0.75 }
percentage_score = { prestige = 0.98 }
percentage_assasination_success = 1.5
pillage_score = { gold = -5 }
}
mountain = no
hills = no
forest = no
plains = no
march = no
desert = no
}
I would say delete the terrain = no and then you should be able to build them. Oh and add some cost and some other stuff.
This way we can just have one of these and add 2 new buildings.
Btw just tested and here we go. All the terrains were listed thus it could never be built in any provinces. Here is the screenshot from my change: