Board Thread:Theories and Speculation/@comment-1512913-20161105081557/@comment-25122992-20161231191219

Hagoromo knowing about BZ is somehow more understandable, since it's possible that Hagoromo had some connection to Naruto/Sasuke, and they were told by BZ about his role in history. Although it can be argued there was no such connection (Hagoromo found out about Naruto's/Sasuke's success only via the seals reappearing on his palms), but the same mysterious way, Hagoromo knew which dimension the saviours must be summoned back from, and that Kaguya/BZ were the main villains, though he didn't ask Team 7 about any details after their return.