New codex means a few more fluff entries, nothing major:
Calendar (listed simply in the 41st. millenium- this might be an indication that specific dates matter less to GW these days)
THE HUNTERS HUNTED Amid the scalding mists of Volghast, the White Scars and the Tau of Vior’la Sept do battle. The two forces stalk each other through the mists, circling and feinting amid the sporadic echo of fierce gunfire. Following the prescient visions of Librarian Kaljuk, the White Scars finally spring a deadly ambush, crippling the Tau transports and massacring their stranded foes wholesale.
(I believe this is part of the Agrellan battles)
THE NIMBOSA CRUSADE Working alongside the Imperial Fists and the Imperial Guard, the Black Templars launch a violent assault to retake Nimbosa from the expansionist Tau. The xenos fight furiously to retain their prize, but after the Black Templars capture their orbital defences, the planet’s Tau garrison is overrun by an Ultramarines assault force.
(I don't know if that puts Nimbosa to rest or if we had this information previously)
Short and... kind of bitter. Not a lot of fluff and just a few more pictures of Tau being blown away per usual.