Realistically speaking, Rodinal doesn't go bad. Seriously. Yes, I can believe if it sat for a very long time that components would separate, but with vigorous mixing, it'll be good to go. I had a bottle that sat, 80% empty, and NOT hermetically sealed, for a good 7-8 years. A good shake, and I developed a half-dozen rolls with the tar-looking substance in the bottle, and they came out perfect.