Also with my story The Mikaelson knows that Stefan is a doppelgänger
The reason why Klaus didn't use Rayna Cruz for his ritual because she was a vampire hunter and her doppelgänger blood wouldn't work anymore so Klaus turned her lover into a vampire and have her killed her before leaving
Also with the travelers they knew about Rayna and Rosalyn so they trapped Rayna in a different body and have the Gemini coven put Rosalyn in the Prison Worlds with the heretics
Sybille de Moretti is the next doppelgänger after Tatia and at this time Klaus doesn't know how to break his curse and century is when The Mikaelson are get used to the