Below are my own personal beliefs about Isaiah 7:14-16 and Matthew 1:22-23, based on the research I have just done.
First, let's have a look at what the Hebrew word for "virgin" or "young maiden" is in Isaiah 7:14:
H5959 - ???? - ?alma^h
Brown-Driver-Briggs' Hebrew Dictionary Definition:
1) virgin, young woman
1a) of marriageable age
1b) maid or newly married
Part of Speech: noun feminine
A Related Word by BDB/Strong’s Number: from H5958
Then, let's see what the Greek word for "virgin" means in Matthew 1:23:
G3933 - pa??e´??? - parthenos
Thayer's Greek Dictionary Definition:
1) a virgin
1a) a marriageable maiden1b) a woman who has never had sexual intercourse with a man
1c) one’s marriageable daughter
2) a man who has abstained from all uncleanness and whoredom attendant on idolatry, and so has kept his chastity
2a) one who has never had intercourse with women
Part of Speech: noun feminine
I believe that Isaiah 7:14 did have an immediate fulfillment. I do not know who the woman was that was spoken of in Isaiah 7:14.
Isaiah 7:14 says (Literal Translation of the Holy Bible): So, The Lord Himself will give you a sign: Behold! The virgin will conceive and will bring forth a son; and she shall call His name Immanuel.
Does that Scripture say that the virgin will be a virgin when she conceives or when she gives birth? I don't think so. It says that the virgin (who at the time Isaiah 7:14 was spoken, was a virgin) would later conceive (which must have been done by having sex with a man).
That makes the most sense to me -- she was a virgin at the time Isaiah spoke those words -- but then she had sex with a man and conceived a child, and called him "Immanuel".
So, it did have an immediate fulfillment (and obviously the people involved knew who that woman was).
Matthew 1:22-23 says (Literal Translation of the Holy Bible): And all this happened so that might be fulfilled that which was spoken by the Lord through the prophet, saying, "Behold! The virgin will conceive in her womb and will bear a son, and they will call His name Emmanuel" (which translated is, God with us).
I believe that Matthew was saying that Isaiah 7:14 foreshadowed and typified the Messiah's birth -- I do not believe that Matthew is saying that the immediate or only fulfillment of Isaiah 7:14 is the Messiah's birth. In the same way, Abraham's near-sacrifice of Isaac foreshadowed and typified The Father sending The Son [Jesus Christ] to Earth to be sacrificed.
Also, notice in Hebrews Chapter 9, it is explained that the sacrifices of bulls and goats foreshadowed the sacrifice of Jesus Christ, and that the earthly Tabernacle and earthly Temple foreshadowed the True Tabernacle and the True Temple, which are in Heaven.
I believe that Matthew was saying that Isaiah 7:14 had an indirect, greater fulfillment in the birth of the Messiah, which was foreshadowed by original immediate fulfillment. I believe that Matthew was pointing out that Mary was actually a virgin when she conceived and when she gave birth, which would have been a greater future fulfillment of Isaiah 7:14, because in the original immediate fulfillment, the woman was a virgin when the prophecy was made, but then she had sex with a man in order to conceive the child. Also, Matthew was pointing out that the Messiah would truly be God With Us [Immanuel] in His Nature and Essence, which is a much greater fulfillment than the original immediate fulfillment (in the immediate fulfillment there was a child born called Immanuel as a sign that "God is With Us", but he was not God With Us by his nature or essence).
I believe Matthew was saying that Isaiah 7:14 was "fulfilled" or "made absolutely complete" in a greater sense, in the birth of Christ.
Can you give me a reason why Isaiah 7:14 could not have had two fulfillments -- One that was immediate, and one that was future, which was much greater? Why could Isaiah 7:14 not have foreshadowed the Messiah's birth, in the same way that Abraham's near-sacrifice of Isaac foreshadowed the Messiah's sacrifice, or in the same way that sacrificing bulls and goats foreshadowed the sacrifice of Christ, or in the same way that the earthly Tabernacle and earthly Temple foreshadowed the Heavenly ones?