Factories of Mass-Production, the modifier given to the province where the Industrialization institution spawns, currently gives the province +1 building slots. While nice in theory, in practice I find this bonus isn't very useful. Since Industrialization can only spawn in a province with at least 30 dev, it's generally possible to build every building you want in the province without the bonus slot from the modifier. By making the modifier also increase the number of manufacturies the province can have by 1, it is far more likely to be useful.
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