Reputable Poster

The company I work for is currently moving from World 8.1 to E1 9.10.
In World, back in 1999 they built a custom file for tracking Harmonized tariff codes, Net Cost Method and a couple of other NAFTA related fields.
The key to the file that was built is Item and Branch.
Looking at E1, I see that Oracle has all of those same fields, but at an Item Master level.

I would assume (perhaps wrongly) that Oracle would have many other customers who have to deal with NAFTA and that is why the fields were added.
We have plants in the US, Canada, and Mexico.(Germany and China) These plants all make, buy, or sell any number of items to each other and to customers all over the world.

Can anyone give me some insight on how they handle the tracking of these codes?
Should these be at the branch level? Or is Oracle right in putting them at the Item Master level?