A dress rehearsal means you are doing everything just like the real performance to see if everything is working fine. That includes costumes, makeup, hair, lighting, etc. That video we have is a rehearsal, not the dress rehearsal. None of the dancers including Britney are in costume.
HIAM is a way better song than Work Bitch. Work Bitch has the same beat the whole way through. So repetitive. HIAM has a climactic build up and it explodes at the end. I wish they did HIAM in vegas