In the past, I know they've brought people back pretty promptly at the mandated 6-month mark if that person contacts the recruiters for the repeat interview. In those situations, the interviewee may only have to repeat the portion of the interview that was unsatisfactory the first time, such as the sim.
Currently, with all of the people waiting for interviews, I don't know if they are putting the same emphasis on people coming back for a second/re-interview.
After your first interview, were you asked to contact them again at the 6-month mark?