Complex doubts about throwing tech

I just realize I’ve got a serious doubt about the grab/throw technique.

In order to throw the opponent after his jump-in - the challenger fails the combo after the jump-in - is it necessary to reinput a back or a forward direction before pressing the button?

Or keeping the back direction, used to block the jump-in attack, is enough to throw the opponent if followed by a button input?

Does the block stun animation reset the command throw sequence?

no
yes
no

Its completely random as far as i know.
Its so frustrating sometimes.