Can't speak to "omissions," but can say that regional practice in that Cathar region during the 1st millenium established a special place for Mary Magdeline in local worship. And at least one local ruler believed himself to be "in the line of David." If memory serves, it was that regional leader who led the first Crusade to the Holy Land and became, for a while and with the support of the Templars, the "King of Jerusalem."
can say that regional practice in that Cathar region during the 1st millenium established a special place for Mary Magdeline in local worship
St. Mary Magdalene was a very popular saint throughout Europe, not just in the south of France. There were no more chapels, churches or shrines dedicated in her honor in southern France than there were in Italy, England, Spain or Swabia.
And the Cathars rejected the cult of the saints entirely - one of the reasons why they were denounced as heretics and one of the reason why some modern Protestants like to pretend that the Cathars were somehow a proto-Protestant movement.
In point of fact, the Cathars believed that Jesus was a pure spirit, not a man, and that the physical world was evil - that all men are trapped in a prison of flesh by the devil. They believed that Jesus was a nonphysical apparition who came to point the way out of the physical world. To a Cathar, the concept of a Jesus who was a real man and who impregnated a real woman and trapped another spirit in a prison of flesh would be unthinkable.
And at least one local ruler believed himself to be "in the line of David." If memory serves, it was that regional leader who led the first Crusade to the Holy Land and became, for a while and with the support of the Templars, the "King of Jerusalem."
Which local ruler was that? Raymond IV the Count of Toulouse? Raymond IV was indeed the most prominent nobleman from southern France in the First Crusade and he helped conquer Jerusalem.
However, he was offered the crown as King of Jerusalem and he refused it. Baldwin I of Boulougne, from northwestern France, was the first King of Jerusalem.
The only primary source surviving that contains a detailed description of Raymond IV by one of his close associates and supporters makes no mention of any claim to be "of the line of David". If he truly believed this, wouldn't he have accepted the kingship of the City of David?
I think you're confusing Dan Brown's fictional novel with actual history.