Supermans creators lawsuit is why nu52 happened. Warner won when the judges agreed the superman creators terminated their rights to get them back. All they own is early superman adventures.
Warner also won for SuperBoy.
Carmine Flash suit is more tricky, he did not work for hires flash costume but did for everything else. Deviations like wallys or even the smaller one don't count. So dc owns them for new material.
As for Neal Adams Batman costume, that's more about fees that only retro product service can afford to give. They can use the carmine one for batman as shown in dc rebirth previews.
Most old costumes are being restored anyways. Ted Kords blue beetle suit, the creeper back in his costume.
They restored Teds career pre doomsday.
Seems they're going for pre inifinte crisis for wonder-woman, considering one book had them mention wondy as new while Superman and batman started way earlier.