Sure.
I think what's happened in Canada—and we started out with this discussion about the dates—is that these have been in place for 10-year periods and have then continued on, generally with little review. For example, the last time was in 2004.
The Doha Round was a relatively new phase, and there was a decision made not to do a review because the most favoured nation tariffs would be implicated and have subsequent implications.
So there's no automatic threshold. The United States, for example, reviews the general system of preferences annually, including beneficiary countries and products on the list.