Okay, from seeing every terminator to the latest, something pops out. If in every movie, in some way shspe or form "Skynet is stopped" why is it just slowed down . so here is my take. Every terminator, man tries to outwit machine, but subsequently machine is a step ahead, then in Terminator Genisys, man uses machine to outwit machine aka skynet by sending the terminator to 1974 to prepare Sarah. This presents issues which were confusing, but i have come up a confusing yet clear resolution.Reese goes to 1984, sent by John under several witnesses hence many volunteered, ultimately Reese was choosen. Reese was suprised to find Sarah not only prepared by a terminator. But effectively two terminators where originally was one. In Reese's glimpse of memories, he tells his former self to stop Genisys from being birn. As we have found Judgement day is inevitable, and as i see it , it will be if they continue to stop it from birth vs "conception". When the timeline is changed for man so the manchine interrupts it because Skynet has still been concepted, otherwise nit terminator would exist in the past. To explain how tge t-1000 made it back with the t-800 in 1984 is when John was over taken by tge human looking Skynet not everyone was killed. Someone remained to activate the machine to redo the destruction of Skynet before they sent back the t-800 and inflitrated the t-800 to go to 1974, however, since the timeline was not interupted but changed by man , manchine was prepared and manipulated it as well, sending the the t-800 back bur thus had to be done more rhan once to perfect it so every time the destruction on skynet got pushed forward so eventually the t-1000 was sent as well. So long story short, i believe the concept or idea of Skynet is the goal to be stopped not the activation. Do when is the true mystery.