> Is the Grade Ipsissimus attained by experiencing Satori?
Certainly not; "satori", in and of itself, doesn't even qualify one to be a
roshi (i.e. a "Zen master").
>In what area/s of knowledge or understanding would an Ipsissimus lack
>if they attained that grade only.
This isn't really even a meaningful question. One can't (at least as I
understand it) "only" attain the grade of Ipsissimus, and such attainment
isn't about "knowledge" or "understanding" in any conventional sense.