You get the 'trading in' bonus is separate from who produced it.
If you produce 20% of a good, but you don't control any of the local trade node, then other countries will get the 'trading in bonus'.
Assume that you colonial nation only exists inside one trade node: if your colonial country produces 50% of the worlds tobacco, and you control 50% of the trade in that node, you should be trading in 25% of the world's tobacco. If your colonial nation controls the other half of the trade, they get the other 25% trading share.
Make sense?