If it wouldn't work for Dream Within a Dream / Assassinate, why does it work for Geirskogul / Nastrond or Earthly Star?

Actually, this is another reason why I created this topic. I want to know why it's seemingly technically possible to combine some oGCDs into one button, but not others.

As far as I understood what was said was if Dream/Assassinate would be combined, and you would press Dream while lagging, it could automatically register as if you want to do Assassinate as well, so you would use 2 instead of 1 oGCD and thus clip your GCD. Or did you mean something else?