Right, there are apostles that aren't part of the Quorum of the 12. For example being part of the First Presidency means you're not part of the Quorum although you still are an apostle. There is some evidence that the Three Witnesses were apostles even though they never were part of the Quorum. They were the ones that selected and ordained the apostles that became the original twelve. D&C 18 talks about how Oliver Cowdery and David Whitmer are to find the twelve and also says this: "And now, Oliver Cowdery, I speak unto you, and also unto David Whitmer, by the way of commandment; for, behold, I command all men everywhere to repent, and I speak unto you, even as unto Paul mine bapostle, for you are called even with that same calling with which he was called." (verse 9)