The fork in the road

Originally the bomb “Jughead” was to be detonated with the intention that by preventing the hatch from being built, the ill-fated Oceanic flight 815 would not crash and the remainder of history would be changed. But since the electromagnetic anomaly originally was there in 1977, blowing up the bomb had to change history from that point on. Even the lives of the survivors were changed from that point on. Evidence for this includes, but is not necessarily limited to, the following:

Sideways Jack had his appendix out when he was seven years old

He is the father of a teenage boy.

James Ford is a police officer and never was a criminal.

Desmond is on Oceanic 815.

Therefore a piece of conventional Lost wisdom has been that when the nuclear trigger to “Jughead” was detonated at the end of s.5 the timeline of Lost was split in two; put differently, the two versions of present reality diverged from a single point in 1977. That’s been rendered invalid now by at least one fact: Roger and Ben Linus left the island before The Incident. Also Sideways Ben is not one of the Others, so he was never taken to the temple, so he was never was shot by Sayid (because if he had been shot by Sayid and not taken to the temple, he would have died). This would explain why Sideways Ben is essentially a grown-up version of the kind, idealistic kid who was taken to the island by his father: if Sayid’s attempted murder of Ben started Ben down the path of evil, well, that event never happened in the Sideways universe.

This indicates that the divergence between Island or “normal” reality and Sideways Reality started at an earlier date than 1977 and I’m going to call it at 1974. That’s early enough for the Linuses to have left the island, but late enough for them to have arrived there. But there’s another reason for proposing 1974, namely…well, think about it. If the hatch was never built, then Oceanic 815 never crashed in 2004 (in fact the island is sunk by then), and none of Lost ever happened. Which means that none of the survivors went back in time to 1974. So the elimination of the electromagnetic anomaly would not change history just from 2004 or even from 1977, but from 1974.