ok so after a bit of testing, i think this is when IH is allowed
an IH is allowed during the point of a normal or move that would be EX cancellable
so for example, the first hit of nanaya 623B can be cancelled into a EX or Arc Drive
so during this first hit, you can IH it
dunno, probably will try more, or someone else can clarify and test
it'll probably take a long ass time for it to be ported, look how long it took B2 to be ported to PC