The Blood Angel codex is out and we have some new lore and information coming with it. Since the Blood Angels and their successors were nearly wiped out in the Devastation of Baal new paths have to be forged for the sons of Sanguinius.
Huge thanks to everyone who sent me pieces of lore on this, huge thanks for the chap who gifted me the digital version of the codex while I await my hardback copy and a huge shout out to Reddit user Dreadnautilus for his amazing post on r/40kLore!