Actually, there would be no K-1 A.E. since El Nido didn't even exist for Serge to live and die (or not, hence the dimensional split. Perhaps just K-2 and K-2', then, to distinguish between the timeline before and after the dimensional split.
Kay.
And to note, Leena didn't send Serge to collect scales "before A.E." That Serge was even alive means that the dimensional distortion already existed.
Not really. Just because Schala interfered, doesn't mean that what she did, couldn't be undone. FATE had 10 years to destroy the Arbiter, AND the Prometheus Circuit. It's just that, FATE didn't know of the Prometheus Circuit, until after it had rid of the Arbiter. This suggests that Wazuki/Lynx, then, interrogated Lucca. Kid seeks revenge, and goes back in time. But, because her older self changes time, her younger self would've dissapeared (kinda like what happened to Marle and the Queen, at the beginning of CT). Thus, is why she is trapped in her memories; the past is rewritten. The dimensions split, interpreting events of K-2 into two categories, only now, Angelus Errare was created from the start. Well, at least that's my view of it.