There are only 5 girls that are hirable through the career book. The other courtesans are hired through the business takeover system
How do you get the 5th girl from career book? And how do you get girls from business take overs (I've taken over 2 so far with no new girls)?
Yeah, I have the same problem. Played pretty far (all girls level C) on Mac and couldn't level up because I never got the 5th girl.
To unlock the new girls you need to: upgrade your establishment (evaluation), build a meeting room, go through the business takeover system
Having the same problem on android the 5 girl hasn't appeared at all