Brass

If you discard a Location card you may build that industry at the named location even if it is not part of your network; if you discard an Industry card you may only build that industry in a location that is part of your network (page 5).

Yes — a Rail Link or Industry tile that requires coal must be connected to a source of coal after it is placed; you consume from the closest connected unflipped Coal Mine (or buy from the Coal Market if not connected) (page 5).

No — consuming iron does not require a network connection: you may take iron from any unflipped Iron Works (owned by any player) for free, or buy from the Iron Market if none are available (page 5).

Shipyards flip when built; Cotton Mills and Ports flip when you perform a Sell action; Coal Mines and Iron Works flip when their last resource cube is removed — flipped tiles immediately advance your Income Marker by the amount shown on the tile, and flipped Industry tiles score VPs at end-of-era scoring (pages 5 and 4).

You may overbuild your own tiles freely, but you may only overbuild an opponent's Coal Mine or Iron Works and only if there are no resource cubes of that type anywhere on the board (including its Market); overbuilt tiles are removed from the game and do not score (page 6).