Is the purification bath valid if one takes it while their hair or parts of their bodies have been wet before?

Answer

Praise Be to Allah and Peace Be Upon His Messenger.

The necessary procedure to have a valid correct purification bath (to impure oneself from Janaba) is to let pure water reaches all your body parts after the correct intention. Being wet before the bath is not a prevention. Once water reaches all body parts even if some are wet, the purification bath is valid.