According to the textual apparatus I have (UBS 4th Edition, 1993), verses 9-11 are in over 900 ancient Greek manuscripts of Mark and missing in only three. In one of those (Vaticanus, I think) the scribe has left a space for the verses, showing at the very least that he was aware of their existence. It is in the 5th Century Codex Alexandrinus and other early uncials.In your gotquestions link the first paragraph said this
"The King James Version of the Bible, as well as the New King James, contains vv. 9-20 because the King James used medieval manuscripts as the basis of its translation. Since 1611, however, older and more accurate manuscripts have been discovered and they affirm that vv. 9-20 were not in the original Gospel of Mark."
So it was not me that brought it up. I addressed your link.