I lean towards Anakin's fate being spin doctored by Palpatine. Savior of the new Empire dying at the hands of the evil traitorous Jedi makes for good press. The truth is far too complicated anyway.

And if you're the boss of the Galaxy, once you bring in the new guy in the scary armor and heavy breathing, nobody dares to ask too many questions.

All Palpy needs to do is introduce Vader as a injured Jedi who had remained loyal.

Tarkin and others know Vader is a former Jedi, but probably little else.