Hymn LXXII closes Book XIX with a simple sacrificial formula about grass deposited in a chest. The proper Atharvaveda effectively ends here. What follows in Book XX is the largely Rig-Vedic recycled material discussed in this commentary’s note at chapter 581. Anyone reading the Atharvaveda as a single religious work can reasonably treat hymn XIX.72 as the actual close — the philosophical capstones (Kāla, Sleep, Brahman) are behind you, and what comes next is a different kind of book. The Atharvan tradition itself seems to have understood this: the Gopatha-Brāhmaṇa (the Atharvavedic Brāhmaṇa) treats the first nineteen books as the core and Book XX as supplementary.