a-dev just opened the can of worms.
I'll try to give the quick and dirty version of my thoughts on this.
As soon as the T-800 arrives in '94/'95, the timeline as Kyle remembers it, and as the T2 T-800 recounts it, is changed by the course of events that will follow. This causes the events leading up to Dyson being the man most directly responsible for Skynet (and everything that is supposed to follow that) not to occur. That means that all the events leading up to the Judgment War, John being the savior of mankind in
that future, Kyle joining the resistance, John and Kyle finding each other, John givng Kyle the picture, Kyle volunteering to go back to 1984, the timing of the resistance to defeat Skynet in 2029--shortly after the Terminator infiltration units ("the newest" "the worst" of the Hunter Killers) start showing up, and the discover of the time displacement equipment which all culminates in Kyle arriving in 1984 to save Sarah, create John, and destroy the T-800 in the Cyberdyne factory, will not happen in the same way if at all. Logically, that means that it's possible that none of it will happen and a totally different outcome may occur, including the failure of the resistance to defeat Skynet and the extermination of mankind. For that matter, the resistance may not ever get formed, and Kyle's parents may not be in the right place to survive the nukes of Judgment War and have Kyle, and John ceases to exist anyway.
However, assuming a similar course of events still does take place, it still could not all happen in the same perfectly timed way to create the scenario that ends/begins in 1984. The solid circular cause and effect cycle of the original timeline established in 1984 and expounded on by the T2 T-800 before Dyson is contacted is essentially erased as soon as contact is made. What lead up to 1984 from the future is now replaced with an unknown destiny where lame-ass characters like Marcus Wright could replace John as the savior of mankind, and John and Sarah are irrelevant.
Point being, James Cameron sold out to make a Hollywood version of his original vision, and it squandered the raw purity of the original concept.