There are so many combinations that an exhaustive search is not feasible – you can see for your gear that we estimate approximately 59 trillion possible combinations. Simply enumerating those would take forever, let alone scoring them.
So we use several algorithms and heuristics that can identify subsets of those 59 trillion combinations that have a very high probability of containing the optimal result. Thus there’s always a chance that a combo will be missed. But the algorithms are designed such that it would be near impossible to miss a combo that scores “significantly” higher than one that was found – if it does happen it will be a case like this where the difference is small enough that it’s hard to prove one way or the other which set of gear is actually better in-game.