Although the tales are set in supernatural world (two of them, at least, I regard The Flood as slice of life), they contribute beautifully to the Narrator's sense of reconciliation.
For some, the lost of main characters' or in-depth background story (especially about the Narrator's behind the scene story before they read the memory lane of the books, there is a potential right there!) sure could make the tales as losing their substantial to the theme, but then these tales also give room of imagination regarding the said background or situation of the main characters to become relatable humane to the reader about the general problems they face in life.
Because in my opinion, whatever your background (age, gender, race, etc of social-cultural status) and in whatever forms the problems take; you may encounter or familiar to a situation in which you are : trying to cope with past, or being "normal", and the options and consequence of running away with it or sharing the burden and bravely face the core problem (Beyond Yesterday's Grasp), escaping terror of beloved ones dying and trying to accept it willingly or coming to the term exhaustedly with time (Let Go), and uncertainty of coming-of-age or your way of life in general (The Flood). May it later be elevating or destructive, they are cautionary tales anyway, aren't they? ;)
And of course, there is this already mentioned problem : the Narrator abruptly told the reader that they had finished ALL of the books (meanwhile I just only had read ONE of them :'D ), so it came as awkward and the epilogue were kind of lost from me for a moment.
Overall, it's an anthology of tales that worth to read and left the sense of relief, even if it's just a little bit. Keep up the good work ^^