I believe that years later, after the publication of the Harp of God, WTC acknowledged that Mary contributed 1/2 the DNA of Jesus, so that he could actually be said to be a human. They also said that in the "conception" that the DNA contributed by Holy Spirit "canceled" out the imperfection of Mary's DNA.
I am sure they are right since they are inspired and infallible in all things. They have never been wrong and never will be wrong - not about anything - nothing. If they were wrong, then they were still on the divine course to what is right. If you feel otherwise, then you are wrong, fighting against God and his Governing Body.
You - Wrong Wrong Wrong
WTC - Right Right Right