Now, I am not a biblical scholar in any way shape or form, so bear with me as I weave my way back in time through biblical versions. (I am certainly likely to skip important concepts and steps here... so if you want to make this short, skip to the bold words at the bottom of this post.)
2011 NAB: "Therefore the Lord himself will give you a sign; the young woman, pregnant and about to bear a son, shall name him Emmanuel." [Why "young woman"... the USCCB states at the bottom of "Sample Change" - "The young woman: Hebrew ‘almah designates a young woman of marriageable age without specific reference to virginity. The Septuagint translated the Hebrew term as parthenos, which normally does mean virgin..." So if it normally means "virgin"... why not translate it as "virgin?"]
1970 NAB: "Therefore the Lord himself will give you this sign: the virgin shall be with child, and bear a son, and shall name him Immanuel." [Seems the 70's had something right.]
1609 Douay Rheims: "Therefore the Lord himself shall give you a sign. Behold a virgin shall conceive, and bear a son, and his name shall be called Emmanuel." [Do we have a pattern?]
Latin Vulgate (Jerome): "propter hoc dabit Dominus ipse vobis signum ecce virgo concipiet et pariet filium et vocabitis nomen eius Emmanuhel" [I am not a Latin scholar]
Hebrew: "כן יתן אדני הוא לכם אות הנה העלמה הרה וילדת בן וקראת שמו עמנו אל׃" [Yeah... I have no clue... I just copied it from some website and started doing google searches for the different groups of characters. I am not a biblical scholar, and I am certainly NOT a Hebrew scholar!]
While this exercise in performing Scripture comparisons was fun, and even forced me to learn a smidgen of Hebrew... the effort really - doesn't - matter. The Perpetual Virginity of the Blessed Virgin Mary is a Dogma of our Catholic Faith. Since the Infallible interpretation of Catholic Church on Sacred Scripture does not and cannot conflict with this Dogma of our Faith... it is very odd that this revision was deemed necessary.