Book of River Nations - Carpenter bonus for multiple cities?

[Valgol]

Book (2nd printing updated) says:

Quote:

Carpenter (30 BP; must be adjacent to a mill; maximum 1 per city; 1 x 2 city blocks): A building for the production of wooden objects and building materials. Reduces the cost of all buildings by 1 BP; Economy +2.

Does this 1 BP reduction in buildings cost apply to that city only? And if it doesn't, does the reduction from Carpenters in different cities stack?

My initial assumption was that bonuses only applied to its own city, until it was pointed out that it says "all buildings" and not "all buildings in same city" (as all the other discount descriptions do). But if it does affect all buildings, then surely the bonus can't stack otherwise you'd just spam Carpenters across multiple cities such that the cheaper buildings then get huge reductions or even come free? Or is that how it's meant to work?

[Philip Knowsley]

I would also point out that it says... 'maximum 1 per city', which you'd
have to say that it kinda hints that it needs to be built in a city for
the BP reduction to apply - in that city.
By the same token, the economy benefit applies to the kingdon - & stacks.