who are "they" ? if its Marines and World Government (except gorosei) then they didn't know single thing. its because the scene on Greenbit. Fujitora didn't even knew Doffy is a CD before Law suspect Doffy that he might be a CD, even Fleet Admiral Akainu didn't even knew any of it Before he stepped into Gorosei's room.
They = Imu, Gorosei and the other Celestial Dragons
Those are the only one that should know.
What is kind nonsense, as Doffy surname Donquixote is the same name as one of the 20 founding families, people from the WG could easily link the things.
But pehaps the names of the families arent public knowlodge and to the outside world the Celestial just use the "Saint" and only between them they use the surnames.
Also Sengoku could know if Rocinante hรกs told him