So...  In my "Blessed be God" prayer book (pre-Vatican II), there are 9 "O Antiphons" making up a novena before Christmas (Dec. 16th-24th).  Yet, everywhere else I can only find a 7 day "O Antiphons".  Anyone familiar with the history of this, have an old book with it as well and/or know why this might be?

In the Roman Church, there are seven of these Antiphons, one for each of the Greater Ferias, They are commonly called the O’s of Advent, because they all begin with that interjection. In other Churches, during the Middle Ages, two more were added to these seven; one to our Blessed Lady, O Virgo Virginum; and the other to the Angel Gabriel, O Gabriel; or to St. Thomas the Apostle, whose feast comes during the Greater Ferias; it began O Thoma Didyme [It is more modern than the O Gabriel; but dating from the 13th century, it was almost universally used in its stead.] There were even Churches, where twelve Great Antiphons were sung; that is, besides the nine we have just mentioned, there was Rex Pacifice to our Lord, O mundi Domina to our Lady, and O Hierusalem to the city of the people of God.

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This might explain it, from The Liturgical Year:
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December 17 – THE COMMENCEMENT OF THE GREAT ANTIPHONS: O Sapientia ~ Dom Prosper Gueranger
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(If you don't have a copy of The Liturgical Year, the whole thing is online here.)