I hope this doesn’t turn into a Lost blog, but I have got to get this off my chest.
I really believe a new time time has been created by the Losties in the 70s.

The Hyrda station has not been cleared of Dharma stuff. The dock (where the submarine was blown up) seems still intact. The barracks were never de-Dharma-ified. The Dharma recruit photos were still on the wall in the orientation building.

It looks like to me that both Dharma and the Others (hostiles) were purged by something our Losties did in the 70s. It’s like the purge in the 90s never happened. Or maybe, the rules were changed when Alex was killed, just like Ben said.