Well OK, Julie. I did not see the show you are mentioning. However, you are correct that there are many gospel accounts. Forgeries? I am not sure where you are getting this from. But it is true that the very dates of some of the documents make this a certainty. These, I would argue, primarily belong to the apocryphal gospels. It is also true that these were well known to the early Christin writers and their comments are available for any who wish to pursue this further. As far as the writings which we have either in manuscript form or mention, the primary ones are as follows, along with their approximate dates or authorship:
Canonical:
Mark 55
Matthew 60
Luke 62
John 80-85
Apocryphal:
Gospel of Thomas 150
Gospel of Truth 140-180
Gospel of the Twelve 2nd century (no surviving fragments)
Gospel of Peter 100-130
Gospel of the Egyptians 2nd century
Gospel of the Hebrews mid 2nd century
Gospel of Matthias 2nd century
Preaching of Peter 100-120
Acts of Andrew 150-200
Acts of Paul 185-195
Acts of John late 2nd century
Epistle to the Laodiceans 2nd-4th century
I Clement 95-96
Epistle of Barnabas 100-135
Shepherd of Hermas 100-175
Apocalypse of Peter 135
One of the ways writings are traditionally dated is by their mention, or lack thereof, of the most important event at the time, the destruction of the Temple, which happened in 70 AD. Note the dates of the canonical gospels. The first three are called the synoptics, because they contain substantially similar material. Every writing has its own agenda. Mark is thought by most scholars today to be the first written because of its length and style. Matthew seems to be very concerned with showing Jesus as the fulfillment of the Old Testament, the reason it is traditionally placed first in the current canon. Luke seems primarily concerned with the earthy ministry of Jesus, especially concentrating on the poor. (Acts was originally the second volume by the same author.) John, however, has a very different emphasis, as Jesus is presented as the Word, as Deity. It is not meant, according to its introduction, to be a strictly historical book. So, even though it was likely written after 70 AD, this would not have been an important book to this author.
To be fair, the date of the Gospel of Thomas is a subject of much scholarly debate right now. But I still believe the date listed above to be fairly accurate. But even a perusal of the dates makes it pretty obvious which are firsthand accounts and which are not.
The common misconception is that Constantine formed the canon. While this is a very popular opinion, history paints a very different picture. For instance, I am not personally convinced that Constantine was a Christian from his own accounts. However, during his reign of 274 to 337 A.D. he not only legalized Christianity but made it official. In so doing he neither did Christianity nor the world a favor. He did, however, find a wonderful unifying force for his empire. This is important to understand because it goes to his motives for calling the Council of Nicea in 325.
This first ever council was called primarily because he feared that the disputes he was beginning to see within the church might cause disorder within his empire. The main dispute was Arianism, the belief that Jesus was a created being. The records of the council indicate a lot of debate concerning the famous phrase, "There was when He was not." This reference to Jesus was declared heretical by the council and thus resulted in the proclamation about Christ, included in the Nicene Creed: "God from true God...from the Father...not made."
The popular version of the council today talks of manuscripts that were burned at the order of Constantine. However, historically there is no mention of such a thing actually happening at the order of Constantine or at the Council of Nicea. The closest thing to this happened at the end of the debate concerning the Arian controversy. The Arian document claiming Christ to be a created being, was abandoned by them because of the strong resistance to it and was torn to shreds in the sight of everyone present at the council.
Also contrary to your assertion, Constantine, and the Council of Nicea, for that matter, had virtually nothing to do with the forming of the canon. It was not even discussed at Nicea. The council that formed an undisputed decision on the canon took place at Carthage in 397, sixty years after Constantine's death. However, long before Constantine, 21 books were acknowledged by all Christians (the 4 Gospels, Acts, 13 Paul, 1 Peter, 1 John, Revelation). There were 10 disputed books (Hebrews, James, 2 Peter, 2-3 John, Jude, Ps-Barnabas, Hermas, Didache, Gospel of Hebrews) and several that most all considered heretical—Gospels of Peter, Thomas, Matthaias, Acts of Andrew, John, etc.
Some modern authors like to purport the idea that the gospels of Thomas and Peter (and other long-disputed books) contain truths that the church vehemently stomped out, but that simply has no basis historically. It is closer to the truth to say that the writings of the early church fathers show that these books were well-known to the scholars at that time. However, records indicate that no serious theologians really cared about these books because they were obviously written by people lying about authorship and had little basis in reality. They were not destroyed. They simply went out of use, other than in isolated pockets of adherents. That is one reason why a council declaring the canon was so late in coming (397 AD), because the books that were trusted and the ones that had been handed down were already widely known. With a few exceptions, the books now considered canon were widely ratified by use, and by scholarship long before 397.
Does this mean that the apocryphal gospels have no value? Of course not. I find them to be fascinating windows into what some of the common thought and theories being tested at the time happened to be. The fact that they fell out of use, though, cannot be laid at the feet of Constantine. Rather, it was due to a coalescing and evolution of Christian thought.