Two spools short

There were twelve spools before the first visit. The sealed bag assigned to Mara contained exactly three.

Mara entered first. Her departure photograph shows fifteen spools inside the drawer.

Leo entered second. He was authorised to take two units and add none. His departure photograph shows eleven.

Inés was third. Her package contained four spools, and her departure photograph shows fifteen in total.

There were no other openings. The photographs were taken after each task was completed and before the next person could enter.