As we know, Evan can change his past to create new lives for him and those around him. As the movie progresses, we learn that Evan's new lives take their natural course until the moment he returns to the present.

Now, towards the end of the movie, when Evan is in the psychologist's office after being accused of killing Kayleigh, the doctor mentions several of Evan's other lives as being "invented" to block out the truth.

If his life took its natural course until that point, even Evan would not have remembered his other lives until then, so how could he have mentioned to the doctor before now?