Many Biblical scholars look for subtle ways to discredit the Bible. Such is the invention of the ‘Q’ document. It is an imaginary document said to predate Matthew and Luke, from which Matthew and Luke drew their material. They theoretically used it to embellish the Book of Mark to produce their own books.
Consider the ramifications if that were true. It would mean that there was a source which was more authoritative than Matthew and Luke which has been lost. The reason given that no one mentions it is that it was confusing, and Matthew and Luke had to make it’s teachings more understandable.
The claim then is that God inspired a work which no one could understand and so the Greeks had to interpret God to man in a way he could understand. Furthermore, it implies that many jots and tittles from Gods word were lost. 
The reason scholars need to believe in mythical scriptures is because they do not understand where Matthew and Luke (and John), many years later, got the material that wasn’t available to Mark.
The answer is plain. The mystery which was hidden from the beginning was revealed through Christ and the cross. The apostles did not get magic knowledge, or a tiny taste of omniscience, but they studied the scriptures in the context of the resurrection, to understand the mystery. The more they studied, the more they understood.  The more they studied, the more the Holy Spirit brought things to remembrance that they had been taught  and so the more they shared.
As mentioned earlier:
- Mark wrote that the story began with the preaching of John the Baptist.  Later, with more time to study, they saw the prophetic riddles extending back to Abraham. Matthew begins his gospel there. With more time, Luke was able to push the beginning of the story back to Adam.  And with the most time, and isolation on a prison island, John was able to push the start of the story all the way back to the first words of Genesis. 
- The differences in how stories are told between the gospel authors tell us how much more they could understand the prophetic riddles of the Old Testament. They were able to correlate even more details concerning the life of Christ with the prophetic riddles. Some details did not need repeated since they were well known from previous teachings.
It is a simple thing to scoff at the myth of the Q-document. It is another to actually produce the additional information from the Old Testament by studying it the way that Jesus taught them to. By studying the ‘new’ material from one gospel to the next, and examining how subjects handled in both are treated differently, we can discern the proficiency with which they could handle the mystery at that snapshot in time. Evidence can be shown they could use the same tools more proficiently, and that they discovered new tools with time.
- Mt 5:18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
- 2Ti 2:15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
- Joh 14:26 But the Comforter, [which is] the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.
- Mr 1:1 ¶ The beginning of the gospel of Jesus Christ, the Son of God; Mr 1:2 As it is written in the prophets, Behold, I send my messenger before thy face, which shall prepare thy way before thee.
- Mt 1:1 ¶ The book of the generation of Jesus Christ, the son of David, the son of Abraham.
- Lu 3:38 Which was [the son] of Enos, which was [the son] of Seth, which was [the son] of Adam, which was [the son] of God.
- Joh 1:1 ¶ In the beginning was the Word, and the Word was with God, and the Word was God.