Emmanuel

Emmanuel is not part of the prophecy of the Messiah - it's part of a prophecy for King Ahaz that God was with His people who were about to be invaded by two rival kingdoms, and this prophecy was fullfilled in 2 Kings 16:9 after being given in Isaiah Chapter 7.

You're half right. This is an example of what's called a dual-fulfillment prophecy, which means that it was made for both the immediate and distant future. Needless to say, Mary was not the first virgin in Israel's history to have a baby. Other examples of dual-fulfillment prophecies include Daniel's prophecy about the desecration of the temple (which happened once in ancient Greece and will happen again in the 70th week) and Joel's prophecy about the sun becoming dark, the moon becoming blood, and the outpouring of the Holy Spirit (all of which happened on April 3 and May 30, 33 AD, and will happen again during the 70th week, signifying the return of Christ/Messiah, and the judgment of Israel's enemies).