The more I think about they lipsynching, the more I kinda realize SM 'maybe' tries not to work the girls' vocal cord as it's almost never that we know the girls' suffer from vocal cord illness and such; SM work their energy and body so mostly they got not feeling well and such, but they rarely had problems regarding vocal cords as when one's vocal cord problem would lead to the company not being able to send the girls everywhere in the world. That's my opinion.
About they releasing the same material, I think it's between what FIRSTKLAS said or SM is so damn cheap they need to stop being super thrift on their artists' musicality
