Board Thread:The Flash discussions/@comment-13895380-20161008202230/@comment-16494441-20161008214317

End of seaon 1 - In regards to the Nora scene, no drastic changes were made. Barry was stopped by a future version, and then has a talk with his mom.

End of season 2 - Future Barry and Thawne are fighting in the house. 11 year old Barry comes in, Future Barry (this Barry has already experienced Flashpoint, which explains why he told Season 1 Barry to stay) takes his 11 year old self outside and leaves. Thawne is about to kill Nora, present day Barry stops him, season 1 Barry fades away because timeline was changed.

End of this episode - 3 month later Thawne comes in after all of the above happens. Timeline changes by him being there. So, end of season 2 Barry and the Thawne that first arrived vanish, due to the change. Then he kills Nora.

To add more to this, and to somewhat explain how Zoom can kill his time remnants (grunts in frustration), because they are connected to the speed force, they can exist even if paradoxically. Because the speed force itself resides outside of the multiverse, acting as the glue keeping it together. Also, leading to the fact that it does not have to follow the laws of the universe.

Imagine it like this: You have a folder with a word document in it. You make a copy of it, placing it outside the folder. You make changes to the one outside the folder, then move it to the inside. Replacing that one. You still have the document, but not the original.