The promise is, however, about the future, which is the point. Consider verse 16.
Not as far as the remembrance is concerned.
John 14:25 These things have I spoken unto you, being yet present with you.But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. 26 But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
He was addressing the apostles and was talking about what He had said to them while He had been with them.