It is interesting that several of the alternative gospels put forth as historical show dependence on Matthew, Mark, Luke and / or John. “…the Gnostic Gospel of Truth (A. D. 140-150, doubtlessly known at Rome when Maricon taught there) cites a body of authoritative books that is [nearly identical with the four gospels.]” This means a body of written Scripture had to have existed before any secret Gnostic Gospels appeared since one of the earliest of these “secret gospels” had to recognize the orthodox Canon in its very attempt to redefine the Christian faith.  One of the gospels, dated in the early 100s, is especially interesting.
The Gospel of Thomas, a “collection of 114 sayings of Jesus,” is well known for its inclusion of material from Matthew, Mark and Luke. Given it was written after them, probably in the early 100s, this shows a dependence on the three synoptic gospels. Craig Blomberg, after years of research, says it like this: “…it is hard to avoid the conclusion that the author of The Gospel of Thomas knew the New Testament Gospels as they now stand…” The Gospel of Thomas does distort the historic gospel message with false teachings common in the Mid-100s to 200s, just like the other alternative gospels.  (Note that this is back-handed evidence of an early date for the gospel writings as well.)
The alternative gospels’ late dating is worth noting in more detail. The Gospel of Thomas, the Gospel of Mary, the Gospel of Peter, and the Infancy Gospel of Thomas were all written well into in the 100s A. D.  The Gospel of Judas was written in the Mid-100s to 200s. The Gospel of Truth was written in the 140s to 180s.  In addition, The Gospel of Phillip was written in the 200s.
Compare that with the dating of the gospels, alluded to before. Matthew is dated in the 50s or 60s by conservatives and 80s-100s by more liberal scholars. Mark is dated in the 60s to 70s or by liberals in 60s to 80s. Luke: 60s or 70s to 80s. John 90s or 90s-100s. ,
John A. T. Robinson, a noted liberal New Testament scholar who helped spawn the Twentieth Century “Death of God” movement, dated all of the gospels earlier than 70 A. D., although many scholars do not agree with him. 
N. T. Wright, The Anglican Bishop of Durham and prolific writer on New Testament history, says clearly:
There is no point in dressing it up: the canonical gospels are early, and the Gnostic ones are late. (By “early,” I mean within a generation or so of the death of Jesus; by “late” I mean no earlier than around the middle of the second century.) … all the signs point to this as the correct analysis… The canonical gospels were being read and quoted as carrying authority in the early and middle second century, whereas we do not even hear of the non-canonical ones until the middle of the end of that century.
The impact of this simply cannot be overstated, and it is not lost on Erwin Lutzer.
If you had a choice, whose descriptions of Abraham Lincoln would you believe? Those of his contemporaries or those of people speculating about his private life or political philosophy one hundred and fifty years after his death – especially if these speculators were determined to put their own political theories into Lincoln’s mouth. 
The next post will conclude this series.
 James L. Garlow and Peter Jones. Cracking DaVinci’s Code: You’ve Read the Fiction, Now Read the Facts. (Colorado Springs, Colorado: Victor Books, 2004), 139-140.
 Komoszewski, et. al. 159.
 Blomberg, Gospels, 264-267.
 Komoszewski, et. al. 159; Erwin W. Lutzer, The DaVinci Deception: Credible Answers to the Questions Millions Are Asking About Jesus, the Bible, and the DaVinci Code(Wheaton, Illinois: Tyndale House Publishers, Inc. 2004), 27; Lee Strobel, The Case for The Real Jesus: A Journalist Investigates Current Attacks on the Identity of Christ. (Grand Rapids, Michigan: Zondervan, 2007), 45-46; Bart D. Ehrman. , Truth and Fiction in the Da Vinci Code: A Historian Reveals What We Really Know About Jesus, Mary Magdalene, and Constantine. (New York: Oxford University Press, 2004), 50, 55.
 N. T. Wright. Judas and the Gospel of Judas: Have We Missed the Truth About Christianity? (Grand Rapids, Michigan: Baker Books, 2006), 78
 Richard Abanes. The Truth Behind the DaVinci Code: A Challenging Response to the Bestselling Novel. (Eugene, Oregon: Harvest House Publishers, 2004), 85 n. 22.
 Lutzer 27, 50.
 Blomberg Gospels 25-26, F. F. Bruce The New Testament Documents: Are They Reliable?, Fifth Edition (Downers Grove, Illinois: Inter Varsity Press, 1960), 12.
 Bruce Documents 12; McDowell Code 24.
 Geilser Systematic 474.
 Wright Gospel of Judas 76, 77.
 Lutzer 28.