The old Agfa Rodinal, which came in small, sealed, one-use bottles, seemed to last forever. There are tales of 20 year old samples still being good. The same can not be said for the current clones, especially those mixed from dry chemicals when stored in larger containers. They can fail in a year or so. A common failure mode is for the developer simply to go flat - no longer work. Color is not an indication. Good Rodinal can be quite dark, and bad Rodinal can be only slightly colored.
As I mentioned further up, the reason has to do with using incorrect quantities and incorrect chemicals. If made correctly, home-made Rodinal or Parodinal will last much longer than one year.