View Single Post
The underlying notion is that you check off sequential items starting at the top of the list and work your way down. When you've finished all of the items on the list, you check off the parent as completed (it isn't shown as available until all of the children are complete, and if you were looking at an available or next action view, it wouldn't even show up until that point).

If you look at the same display on the iPad or iPhone app, where you don't get grouping in big chunks like you do on the Mac as you go farther out, but rather day-by-day groups, it is more apparent that those actions not showing a start date become available on 9/15—in fact, the only way you can tell that they don't have their own start date assigned is to look in the inspector.