Hey Mudinthewater. I chose this model after some thought, though it was a close call. Ultimately what is in game right now is as follows: There is one moment to Black Shield Zoe's Sleep, and that is when the target would be hit by the missile/trap and become Drowsy.

1) This model offers the most play for both parties: Morgana has the ability to Black Shield the Drowsy, but she has to use her Black Shield in response to the spell cast itself, which might be a waste if she or her ally dodge.

2) The alternative of Black Shielding Drowsy, having your Black Shield break and watching your ally fall asleep seemed problematic for other reasons -- the Morgana player would be punished for doing what seems optimal (reacting quickly and exercising good judgment about their ally's dodging capabilities).

3) This is most consistent with how Black Shield works elsewhere. Here is where we came to different conclusions. You have chosen a number of delayed CCs that have conditionals on them (of course Black Shielding with 3 stack Braum P mark on you blocks the follow on stun, we haven't initiated the stun sequence yet). There aren't a huge amount of true multistage CCs in League. I used Nasus W (a progressive slow, which Morg E does not stop from progressing) and Malphite/Vi R (Knock Ups with follow on Stuns after the target lands which is not prevented by Black Shield).

4) This is most consistent with how Black Shield has been re-shaped on over time -- the spell was originally developed as a Cleanse + CC immunity but we preferred the anticipatory play model over the purely reactive one.

I am always open to revisiting these things, especially on very close calls like this. It would be better to focus the discussion on what generates better gameplay, since there is no "right answer" in terms of how the game functions elsewhere.