basically the programmers were a bit lazy in scheduling (i can't blame them) and insert an extra game here and there to make everything fit. in all honestly, there is absolutely no possibility of this being necessary, because of the number of unscheduled sims and thus the extraordinarily large number of acceptable solutions. however, in 3 minutes, i haven't been able to solve the problem with a clean algorithm, so it must not be that easy.
for any math geeks, it seems a hack on bipartite matchings would probably get you there. the assignment problem is similar, but breaking it down into 10 assignment problems would only solve each game at a time - potentially leaving you with no solution to one of the last assignment problems. i would guess that if you started with the assignment problem with the fewest number of edges in the graph, and went like that, you would get a clean schedule more than 99.99% of the time. but a perfect solution seems similar to the vertex covering problem which is NP complete and thus (as far as we can guess today) is impossible to solve in a reasonable time frame.
in the end, i am convinced a moderately clever brute force could get you to a proper schedule. i mean after all, real life people get it to work.