MY FACTS:
1) Kings nor Samuel are part of the Septuagint.
2) There were disagreements among the early church father that the Septuagint was even "inspired". It was left as appendices because of the disagreements.
3) The Hebrews never accepted the Septuagint as "inspired", only historical.
4) The Septuagint is not a biased Catholic source.
5) The Septuagint was deemed "inspired" by the Council of Trent in 1500+ AD.
6) No matter how many times you try to bring up this verse in Kings (Samuel), the fact remains this is not how it is in Hebrew (which is far more accurate than the Greek). Even the Catholic Douay-Rheim Bible doesn't translate it as you're translating it.
I don't think you are understanding my point. I am not here to argue whether or not the Septuagint was inspired. I don't even want to argue whether it was historically correct. Let's say that it has no more to do with religion than a government document written in Greek in 250 B.C.
The reason that verse is so important to the discussion has nothing to do with it's inspiration, it has to do with the language it was written in.
The language is greek. It is a clear example, as are the others laid out previously, where the Greek word "heos" does not end the action in the clause preceeding it. The place where the text is found is, in my opinion, important (due to the fact that it was writing that the writers of the new testament would have been familiar with), but it is not THAT important. If that sentence were from a government document, as I stated before, it is still an example of the usage of the greek word "heos".
You are arguing from the language that because of this word "heos", Mary must have stopped being a virgin after the birth. This does not hold water, regardless of what you think of the Septuagint. You don't need to prove that these men who translated from Hebrew to Greek weren't inspired, you need to prove that they didn't understand Greek. And when you have proven that, I have quite a few more quotes from Greek sources where "heos" does not mean what you are claiming it means in every situation.
Again, try to argue against the perpetual virginity of Mary, if you be so bold. But to base your argument on the word "heos" meaning that Mary must have stopped being a virgin after Christ's birth is to build your house on quicksand, it will not stand.