In the adventure "Storm King's Thunder," the players have the opportunity to raid the castle of a cloud giant lady, Countess Sansuri. She is a powerful wizard who has researched a custom version of the simulacrum spell that is capable of creating multiple copies with a single casting (her spellbook is in room 21, the Library, on page 197).
The way it's presented leads me to believe that player-controlled wizards are supposed to be able to copy the modified simulacrum spell into their own spellbooks and cast it if they so choose; however, it never says how many duplicates it can create. The base spell says that you can only create one copy, and that "If you cast this spell again, any currently active duplicates you created with this spell are instantly destroyed." Should I take that to mean that the upper limit on the number of duplicates createable using Sansuri's Simulacrum is the number of aarakocra simulacra inside Lyn Armaal?
18 if my count is right - four in Area 1, two in Area 11, six in Area 26, and six in Area 29