Responses
In the novel, there are indeed timelines (or dimensions), but it was not implied that the 1st timeline Athy, Korean Athy, and the current Athy has the same soul. Like, all of them do exist but only Korean Athy & the current Athy is connected.
However in this manhwa, Spoon is implying that they all might share the same soul - judging by the flashbacks that wasn't mentioned in the novel The Lovely Princess that Korean Athy read.

There are no concrete spoilers of the webtoon since there are a lot of differences the author has made from the novel. Also, beware of false novel spoilers, there are a lot of them around.
One false novel spoiler is that Jeannette sacrificed her life to turn back time. No such thing happened in the novel.