+1 What you said makes complete sense based on the way the wizzard actually works and thank you for your post. However, that is in direct conflict with the TT description of 'What is a Distribution' ---> "... Distributions can also be made from the original assets or principal left by the decedent or maker of the trust." [original assets or principal being corpus].
I hope someone from TT reads this and they update their wizzard to clearly ask for DNI/IDD and specifically indicate to not inlcude corpus. Or if they include corpus, then they need to wizzard for breaking it out on 1041-A-L4. I spent more time than I wanted to deciphering this ... including reading the 1041 pdf from uncle sam. That's another story, but I think the outcome is the same.