RoS - Visual Dictionary
A few interesting tidbits...
*It does seem to make the distinction that Snoke was independent from Palpatine to an extent, but was still, obviously, a puppet:
"Snoke has tested Kylo Ren's worthiness as a disciple, and unbeknownst to all, his capacity to inherit the Sith legacy. Snoke is no Sith, but his role has been designed by the Sith Eternal cultists to act as a final crucible, to groom and mold Kylo Ren into a master not only of attack, but also cunning."
*It mentions multiple times that Palpatine(as we know him) was in fact killed at the battle of Endor, and implies that he was resurrected by the Sith loyalists through "a mixture of technology and the occult." Palpatine himself was not given his own entry in this, however.
*It mentions a few ancient Sith worlds, including:
-Moraband/Korriban
-Malachor
-Ziost
-Jaguada
-Rhelg
*It mentions a few ancient Sith Lords, including:
-Revan
-Andeddu
-Tanis
-Tenebrous
-Phobos
-Desolous
*It mentions a few factoids from the ancient Jedi texts(written by Jedi Master Odan-Urr), which describe the "Chain Worlds Theorem", also known as The World Between Worlds, or Vergence Scatter. Has a "Phases of Mortis" solution, which solves Master Thorpe's "unsolvable" Hyperspace plotting conundrum. Etc.
I'm sure there's more I'll come across, but that's what stood out after my first skim through...