Afaik, it's all versions of the game, not just GS. But, I think you're missing my point though. There are no production modifiers for Medieval naval units. The same modifiers for Maritime Industries are also attached to the Press Gangs PolicyType. Same goes for International Waters, which also has both of the previous sets of modifiers attached to it. But since there's nothing for Medieval that's why none of these policies give a production bonus for it.
I have 3 medieval naval units so I added modifiers for Medieval naval to Maritime Industries and then also attached those to Press Gangs & International Waters.