See, I considered that, but whereas he wouldn’t have known about it while helping Leia escape, the Rebellion probably would’ve gotten word by the time Luke is flying the mission to destroy the Death Star. And that’s probably a pretty big deal at the base.

It’s never confirmed, of course, but I imagine information travels fast within the Rebellion if they were able to steal the Death Star plans. (Edit: Especially given Bail Organa is still alive when the Senate is dissolved.)

At the point he’s actually in the Rebellion, he probably at least already knows that the Galactic Empire is done pretending it’s a democracy.