rules say
If you have multiple buildings or organizations in a settlement and they can generate the same kind of capital, you don't have to roll for them separately—you may add all their capital modifiers together and attempt one check for that kind of capital
My question is why would anyone ever do that? If you control 2 buildings that both give +3 good than if you roll separately you average out to 2 goods earned each of them earning 1 with a roll of 13. If you roll them both together then you get 1 goods from a roll of 16. The thing is for every separate roll you have you are able to add a d20 on to the result, but if you add them all together you only get to add 1 d20 to the result.
Was this intentional? A sort of tax on people who can't do math.