Saul, David, and Errors in 1 Samuel 16-17?

In the story of David's rise in Israel there seems to be a discrepancy in 1 Samuel 16-17. In chapter 16 the narrative tells us about one of king Saul's servants recommending David (Jesse's son) to play music for the purpose of combating Saul's evil/bad spirit/mood. However, after David defeats the Philistine Goliath, Saul asks …