Posted by: Puck
When Landen was eradicated, two timestreams diverged: in one, Landen died in the car crash when he was 2, Thursday is the only one who remembers him, and Thursday goes to live in the WOLP.
Meanwhile, in the other timestream Landen was never eradicated, and he doesn't understand why Thursday suddenly left for the Well without him.
Conveniently, each of them only exists in the "real world" in one of the two timestreams during that time. Imagine how confusing it would be if Thursday had stayed in Swindon while Landen was eradicated, and then had to deal with two different versions of what she had been up to for the past two years!
(All of the other characters are relatively uneffected by the eradication, so their lives are identical in both streams. Except for Billden -- perhaps it's wise for JFf not to try to deal with that one, it would be a little messy.)
To put it another way, during the two years Landen was eradicated the "real world" was unchanged, but Thursday's consiousness was shunted into an alternate universe in which Landen died in childhood. When he was uneradicated, she returned to her original world and had some explaining to do.
Metaphors be with you!