There is the International Merchandise Trade Statistics: Compilers Manual, which we all try to follow, but there are different trade systems as well that can be applied. In Canada, we follow what's called the general trade system, which means that our customs boundary basically agrees with our physical border. In other countries, such as Mexico, they have the maquiladoras, and those are considered to be customs-free zones.
So there are different ways of compiling trade. To reconcile all of that, if you want to deal with one country, you have to do a bilateral reconciliation with that country to try to understand some of the issues that are there, come up with what would be a commonly agreed upon list of issues, and then maybe struggle to come up with a common series too. You have to go into that with a very clear set of objectives of what it is you're trying to accomplish.