The Books in the Bible did not fall from the skies and robotically assemble themselves into the various chapters and verses. Among the thousands of manuscripts, texts, and written evidence, the Holy Spirit bestowed upon the Catholic Church to sort out and put together what is the true Word of God, while casting aside hundreds of other questionable or contradictory writings. This process took nearly three hundred years beginning with early Church fathers and successors to St. Peter.
That authority of the Holy Spirit to locate, cite, and interpret the true Word of Christ did not suddenly disappear with the advent of the Lutheran heresies. This is why the Church has among its adherents, thousands of scholars and theologians who have become converts from every other faith and religion under the sun.
Well sir, whoever compiled the books saw fit to include the passage from Mark, and this one as well, from Luke 22:31,32...
“And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat: But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren.”
The Lord just made it clear right there, that even after the disciples ate the bread, and drank of the cup (verses 19 and 20), they were not yet converted. The conversions would happen after the Lord ascended, for the Holy Ghost would not come until the Lord physically departed. (John 16:7)