That would work for Mexico against USA, but if I wanted to do it for Trinidad and Tobago against Costa Rica, and I couldn't find a list of their head-to-head games, I would have to spend time getting the information from ELO's list of all the games played by Trinidad and Tobago or Costa Rica (I could pick either one to look at). If I wanted the head-to-head results between each pair of the 12 teams in the WCQ Semifinals, that would be 66 pairs of teams. If you know of a website with a list of head-to-head games between any two members of FIFA who have ever played each other, please tell me. I don't mean to be rude. I'm just saying that the information I want can be time-consuming to gather.