Originally Posted by
xX908Xx
Right, so I did some tests of my own and I'm 99% certain that they only apply to their own region, and not the whole province. I say 99% because I could have done something wrong, but I don't think I did. I compared two industry buildings in 2 different regions in the same province (with the 2 regions having a difference of 2% in industry potential) and then checked the bonuses that the income of the buildings got, in the province details screen. And guess what, one had a bonus of 23% and the other 21%, so I guess that is it.
This is my first ever thread in this forum so I don't know if I should delete it now that I found the answer. Guess I'll leave it here if anyone else has the same question.