Well, the point of discussion is, of course, whether the time travel can affect any events earlier than 1973. Such as the birth of Angel and Jubilee.
That would seem to be illogical.
However, In DoFP there was a part where Hank/Beast spoke of ripples in the river of time - although the flow would correct itself. Ripples go in all directions.
The only other get-out clause for this scenario is what's called retro-causation, 
retro-causality or 
backward causation. Normally, we experience cause and then effect, but this is a hypothesis that suggests the effect of something can happen before the cause. 
It's all complex and speculative but if, somehow, this happened, then some things EARLIER than 1973 would have been altered.
Normally, this is considered a separate thing from time travel. But we have to bear in mind that DoFP did not deploy the traditional concept of physical time travel (it was instead done with a consciousness) and also that all this is theoretical and time travel has, to our knowledge, never been achieved. 
If all that feels too much and too forced, then just accept it's a creative retcon.