Verse-end correspondence may rest on a shared letter, or an entire sentence may return in several places. These are different devices: the former primarily connects sounds, while the latter also recalls an explicit meaning.
In al-Raḥmān and al-Mursalāt, recurrence is not mere ornament. After each fresh blessing, argument, or warning, a central truth is renewed. Repeated discourse in al-Qamar similarly intensifies the message at successive stages.
Analytical distinction: ask not only how often an expression appears, but what precedes and follows each occurrence. Its rhetorical work depends on that evolving context.