Since WORLD items exist in the NW and some of YGGDRASIL's lore in the NW became/are true such as the lore about Doppelgangers using telepathy to read the surface thoughts to improve their impersonations, It's possible that the lore about the WORLD items, the remnant's of the last 9 leaves are continued to be hunted by the WORLD Tree Eater in the NW too.