In Terminator 1, during Reese's questioning, the following dialog takes place:
Doctor - Why did terminator kill the other two women?
Reese - all the papers and archives were destroyed during the nuclear war. Skynet did not know anything about the mother of John Connor, it did not even have a photo of her. It only knew the name and the city. So terminator acted like any machine - systematically.
And this brings the logical and the biggest question of all time. Why could John Connor not simply change his name after the war with Skynet broke out? In that way, Skynet would never be able to trace him or his mother in the past.