No, those were both tied to very specific events and can't be exchanged for anything.
So I started playing Maplestory again a month or so ago, and am trying to clear out some stuff from my inventorythat may or may not still be needed. At this point is there any point in keeping stuff like the Cygnus Knight Books or the Slightly Polluted Rocks?
No, those were both tied to very specific events and can't be exchanged for anything.
Spoiler!