I don't dispute all that you say, I just add that I think Mary gave birth, physically. And because we are dealing with something miraculous on all levels, I don't think that it would have caused her to become unvirgin in any way.
I rather think a veil of modesty should, and will forever, conceal the gynecological details of Mary's birth-giving. And I agree, it would not have caused her to become unvirgin in any way.