[Geoff Bacon]

Collections have a single entry per song and are typically sorted A-Z. A song can only exist once in a collection (although it could be n multiple collections)
Set Lists are ordered lists (typically sorted as "Manual") and may contain, as you have found, the same song more than once. This allows playing the same song at different positions in yur performance.

itsme is suggesting that you still use a set list; you just temporarily sort it in A-Z order.
Having eyeballed and removed any duplicates, you then revert to a manual sort (this maintains your previous sort order - apart from not knowing which duplicate you removed)

Geoff