Scripture is only that which the Holy Ghost will witness to our souls thereby sealing it as truth.(D&C 68:4). So when we read the scriptures, (as in canonized scriptures) or hear the words of prophets like you or me or LDS church presidents, we listen for the witness of the Holy Ghost which bears record to us those parts that are scripture for us. As we get more witnesses, our personal library of “Witnessed/Sealed Scripture” grows. Not because more is said, but because more is witnessed by the Holy Ghost as scripture. In this way, the Holy Ghost teaches us “ALL THINGS”, not just some things, and we NEVER have to rely on our poor fellow mortals.