Okay, yeah.
Code:
Trait_YieldChangesPerTradePartner
This is only given for each trading partner.. So if a player has 100 trade routes with the same civilization, they only get the bonus once. I don't remember now if it is dumped into the capital or just assigned directly at empire level and so only shows on the top ribbon of the User Interface.
Code:
<Trait_YieldChangesIncomingTradeRoute>
Is applied to the other player, not the one owning the specified trait.