It's my impression that GTD recommends hard edges between the 5 processes.
When you're working from your next action list, I would guess that you should not try to be organizing at the same time. E.g., I finish action X. If I do nothing special, when I get to my weekly review, I'll figure out what other actions need to be put into my action list.
However, what I'm actually doing is finishing an N/A, brainstorming next steps, organizing. Doesn't feel very productive.