It's extremely likely to be the case, but if you haven't searched the entire space you can't make that assertion with 100% certainty. To put it this way: if I said there is no private key for an address, you couldn't disprove that claim unless you found a private key that gives that address. I do acknowledge that the chances for this to happen are very close to 0%, but there's an (inconceivably) small doubt that there might be an address without any private key.