Not understandable is why INNO didn't just say the building produces a number of random goods from the older era.
Probably because saying that the building produces unrefined goods starting in Modern Era is the same exact thing. You all are just making this too complicated...or you just don't understand simple English. The very definition of "unrefined" goods is "goods from the older era", with the older era being the specific one necessary for your current era's goods buildings.
Unrefined goods = Older era goods required to produce goods in goods buildings in Modern Era and above. Unrefined goods for each specific goods building are from the third era previous to the goods building's era.
Here's a chart for your reference:
Goods building era-Unrefined goods era
Modern-Colonial
PostModern-Industrial
Contemporary-Progressive
Tomorrow-Modern
Future-PostModern
Arctic Future-Contemporary
Oceanic Future-Tomorrow
Virtual Future-Future
Space Age Mars-Arctic Future
Space Age Asteroid Belt-Oceanic Future
Space Age Venus-Virtual Future