Here is the third to last paragraph of the article How the Portugal Draw Boosts the U.S.’s World Cup Advancement Odds from FiveThirtyEight (emphasis added):

So, why I do I say that our 76 percent figure might slightly underestimate the Americans’ chances? One reason is technical rather than soccer-related: Our simulation was programmed to resolve ties beyond goals scored and goal differential randomly, rather than looking at head-to-head results, because the head-to-head tiebreaker so rarely comes into play. But if a Ghanaian win in Brasilia and an American loss in Recife come by exactly the same scoreline — e.g. Ghana 3, Portugal 2, and Germany 3, U.S. 2 — that would trigger the head-to-head tiebreaker. The probability of such an outcome is low, but it means the simulator has slightly underestimated the U.S.’s advancement prospects, perhaps by 1 or 2 percent.

I understand that this rarely occurs, but why not add the one or two lines of code needed to add this?  If they really believe that their probabilities are off and could be easily fixed, why not do it?

Cheers.