Adding to the roster or replacing those who have left?
Recruiting isn't successful if those that are recruited then leave again shortly afterwards.
I used to see a girl at BRM who called herself Emily and she would often complain about feeling "Like a zombie" because of the long hours she was asked to work, sometimes finishing at 4am then back in at 10am the same day for another shift. There was also another girl, Melissa, I think, who was FAF and genuinely 19 years old. I saw her a few times, but, after a few months of her being there, I called in one day and when she was called out with the other girls for me to view she was almost falling asleep on her feet. She left not long after.
I don't know how much say the girls have over the hours they work there and things may have changed in the meantime. I guess the more staff they have available the fewer hours each girl is asked to work.