I think that is mentioned in the novels. A Rebel cell in one on the non-human quarters got word, staged a celebratory protest, knocked down a statue (and a few Stormtroopers), and than got totally crushed by the ISB and more Stormtroopers. This was explain in one of the later novels. The Stackpole ones were before the Special Edition came out.
The idea that the Rebels did get word out that Palpatine had been killed at Endor did force the propaganda machine to acknowledge the Emperor's death, which is why when Rogue Squadron arrived some two years later, the propaganda film gave a presentation as Endor being something like Palpatine sacrificing himself for the greater good.
The idea that the Rebels did get word out that Palpatine had been killed at Endor did force the propaganda machine to acknowledge the Emperor's death, which is why when Rogue Squadron arrived some two years later, the propaganda film gave a presentation as Endor being something like Palpatine sacrificing himself for the greater good.