There are several levels (below) and the full rules may be found at the link above.
Déjà vu: Reread 4 books
Feeling Nostalgic: Reread 8 books
A Trip Down Memory Lane: Reread 12 books
Living in the Past: Reread 16+ books
I'm just going to go for Déjà vu: Reread 4 books. If I find myself doing more rereads, then I'll level up.