Quote Originally Posted by Steve Roberts
...I'd like to know whether this refers to just full, unopened bottles or to half full bottles with a certain amount of air in them.

In my experience, it doesn't matter. I take out what I need and just re-cap the bottle. No squeezing air out, no adding inert gasses, no decanting into smaller bottles...just use the stuff and put the cap back on. My Rodinal progresses from virtually clear, to the color of Chablis, to the color of diet coke, to the color of espresso, all without a change in effectiveness. The only reason I put the cap on is to stop any chance of spillage.