Distinct timelines were inherently distinct possibilities in history.
A minuscule time fragmentation had an insignificant impact on history as a whole. It didn't matter even if it existed in parallel.
This was analogous to a low-budget sci-fi flick that William had viewed in the past—owing to the impact of a colossal comet, numerous subtly different parallel worlds momentarily converged before diverging again. People only realized the many disparities in their memories when scrutinizing their recollections subsequently.
A small-scale time fragmentation wouldn't have a grave impact, but a large-scale time fragmentation wasn't such a benign thing. Not only would it instigate severe chaos in the annals of history, but it would also trigger a lethal time paradox everywhere in the world owing to the shattering of logic.
For instance, Ravenwood's time fragmentation.