Twitch fade with NDNMB

Just wondering if any of you knowledgeable folks out there can give me simple explanation for this one:

Presence of fade w/ NDNMB during tetany/TOF vs absence of fade w/ DNMB (Phase I) during tetany/TOF.
The only good explanations I have found for this action are as follows:
1. Fade is present during tetany/TOF w/ NDNMB b/c of the depletion of Ach at presynapse.
2. Fade is present during tetany/TOF w/ NDNMB b/c of presynapse receptor inhibition of Ach release--much like the presynaptic alpha-receptor inhibition of NE release at the sympathetic terminal?
3. Fade is absent in the DNMB during tetany/TOF b/c of the inhibition of repolarization produced by sux.

Does this sound reasonable?

My other question is this---if there are available receptors at both inhibited nicotinic cholinergic post-junctional receptors, why can't sux have fade like panc or roc?

I would really like to understand the physiology behind these differences, so any help would be appreciated.

THX---Sam

---Post edited for clarification