As the second season of SNW demonstrated, time travel in Trek is firmly rooted in the ‘big ball of wibbly-wobbly timey-wimey stuff’ theory. Contradictory time travel shenanigans happen all the time. The random accidental time travel, sporadic deliberate time travel, perpetual temporal war, and ocassional bored god-like being have really done a number on the universe’s temporal cohesion. They probably have less of a timeline and more of a time-bowl-of-spaghetti.