What two biblical incidents tell of Saul meeting David?

A:1 Samuel 16:13 tells of Saul meeting David, son of Jesse, and of Saul anointing David with oil. 1 Samuel 16:21 says that, Saul having sent again for David, David came to him and became his armour bearer.

1 Samuel 17:31-32 says that David came to Saul, proposing to slay Goliath, and Saul gave David his own armour. 1 Samuel 17:58 then says that after killing Goliath, David came again to Saul, but Saul did not even recognise him. The author of this particular narrative seems unaware that elsewhere in the book, David had already been the king's armour bearer and then his personal musician.