Yeah, the problem with that is it's all theoretical and by fans, and not necessarily accurate. The fisrt few times stuff was calculated up based on dates given just for the 4 avatars pre-Aang, there was major avatar overlap. Byrke admitted to not having done all the math on the avatar timelines early on, so fans making time lines pick and choose based on conflicting "canon" writeups.

I mostly just try to gloss over it, because it is inconsistent.
*shrugs*
I like my ideas, and I'm sticking with them.