It may not be possible to check all of them, but it certainly is possible to check one of them...any one of them. And whichever one you choose to check, you'll find that it exists. So if you claim that some of the possible configurations don't exist, you're claiming they'd have to be among the ones you don't choose to check. But wait, this implies that your choice of which one(s) to check somehow affects which ones exist. It sure would be spooky if that somehow turns out to be the case, which I doubt.