The problem is that the Gospels were written with the Old Testament in mind, and the writers drew intentional parallels between lines in Isaiah and the Psalms and the narrative they were writing down in their own books.
It is hard for us then to discern how closely the actual history fulfilled the prophecies of the OT, since the authors were self-consciously writing it to make those parallels obvious for their Jewish audience.
For instance, Matthew 1:22-3
>So all this was done that it might be fulfilled which was spoken by the Lord through the prophet, saying: “Behold, the virgin shall be with child, and bear a Son, and they shall call His name Immanuel,” which is translated, “God with us.”
references Isaiah 7:14
>Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call His name Immanuel.
Compelling. But let's look at the translations. The word that is translated as "virgin" in Isaiah 7:14 is the Hebrew word almah. The term almah refers to a woman of childbearing age, and does not actually have any connotations of sexual status in the original Hebrew, and is in fact used in Proverbs 30:18-20 to refer to an adulterous woman. Similarly, Isaiah himself used the explicit Hebrew word for virgin, betulah, five times in his writings, but used almah only once.
Now, why would Matthew translate use this to foresee a virgin birth if the word does not actually mean virgin in Hebrew? Because everyone would have been using Greek texts of the Old Testament in his time, as the Jews in Palestine did not speak Hebrew. The Greek texts translated almah into the Greek word parthenos, which does in fact mean virgin.
Greece and Rome ;^)?
It'll be very interesting to see how China turns out.