I understand that. What I'm trying to understand is when is the earliest it could have started and when is the latest it would have been finished.
It couldn't have started before the last of the texts were actually written because the author was still around to correct any misinterpretation. It must have been "finished" by the time of the council of Nicea as that is the time that nature of the incarnation and resurrection were settled.
You're positing that the Church, over time, came to misunderstand its own scripture. The only evidence of this that you've offerred so far is evidence of a development in doctrine during the time that the writings themselves were taking place. But if your theory is true, then the misinterpretation couldn't have started until after the writings, unless the authors themselves were misunderstanding what they were writing, which doesn't seem plausible.
How can you use writings that were completed before the process started as evidence of the process itself?
I believe the process was started before the completion of the last of the canonical texts. Is this so hard to believe? Consider that there WAS no established canon at the time. All kinds of gospels and writings were circulating throughout the Christian communities of the Roman Empire. All kinds of ideas that were later condemned as heretical were also circulating. It took hundreds of years to hash out what was to become orthodox doctrine.