YAWN
You are still talking about a prophecy being fulfilled within a book you have yet to evidence the authenticity of. It seems a little weak that the only evidence you have for your claims is a compilation of books, that have no corroboration from any sources independent of the christian church.
To give you an example.
I could write several different gospels, all claiming George to be the messiah promised in Isaiah (Assuming for the moment Isaiah is even prophesying anything in the first place). I could then go ahead and sprinkle my gospels with catch phrases being stated by George, including actions and deeds as required per Isa. I could even have George become resurrected.
Then I could go around, and say that I found these gospels that written a few years ago, and had them revealed to be true to me, after a religious experience in which the resurrected George admonished me for persecuting the Georgians. I would then go on to right my own books, and create my own Church of George.
That's the problem with your example, everything I just did would make George the Messiah. I could even cite Isa just like you are to show how it became fulfilled! All this would have just as much corroborative evidence as the early christian stories would.
Do you really think the early Christians had no knowledge of Isa? Do you really think that it would be beyond the despot Roman funded Council of Nicaea to cherry pick the gospels that included references to Isa, to make their savior seem more legitimate?