Some Bible scholars consider 1 Samuel 17:12-31 and 17:55–18:5 to be later additions because these verses are not found in certain copies of the Greek Septuagint.,
The WTBTS claims that these do appear in other authoritative copies, so what is the story and background on these scriptures, Saul, doesn't know him, then Saul knows him, then again Saul doesn't know him.