User blog comment:Xilinoc/Ch. 672 - Son of Darkness/@comment-3423279-20160502172315/@comment-1970092-20160503190034

Actually, Yhwach seen the new Zangetsu. Plenty of times, in fact. Do you recall him and Ichigo clashing a bit before Yhwach kicked them out of the Soul King Palace?

As for the Almighty's accuracy... I tend to view it as a power that sees all (or at least many) possible futures, not just The Future. So, in the case of Haschwalth, he clearly didn't forsee everything Uryu would do. Yhwach is obviously much more experienced in the power, and is used to whatever future he sees as being the one that actually happens. That said, I do believe that his dream was just that: a dream, not a vision~