But then Darth Vader sending the distress signal and all aboard were killed. Get’s contradicted by that.
No, the ruse with the distress signal was for the benefit of the senate:
Send a distress signal and then inform the senate that all aboard were killed!
The senate itself was dissolved by the Emperor not long afterward. So it’s quite possible the destruction of the Tantive was never reported.
The Distress Signal is indeed for the Senate but nobody would ever admit that Leia “The Imperial Senator” was sent by Alderaan to be involved in a plot to Destroy the Imperial Super waepon of mass destruction. If anything this collusion and deceit by the senate was probably what caused it to be dissolved as it became clear that the Senate or parts of it was plotting against the Empire in some form of Rebel Alliance.
The Empire wanted the Senate to believe Leia was dead. To send a clear message to the mutineers. Although they would not let on that they have Leia held captive.
According to Anyone from Alderaan Leia was alive and well on Holiday by the lakes and mountains. She was never on that ship… But the Empire knew she was. And they pretended she was killed for the conspirators.
Why else would you sneek about with a hood on if you were not meant to be publically known to be there but in “Secret”