When I bought my darkroom sets, I additionally acquired two powder developers, being XTOL and D-76.
I have only ever used Rodinal (Adonal) to develop my negatives, so I know little of how well such powder developers last stored unmixed.
I don't know of any production or expiration dates, but they are sealed in their original boxes and thus have never been mixed, and have been stored in the dark. Some of the paper I got together with the developer came from the 80s, but since the packages don't look all too old and worn I doubt the developers are that old. It is likely to be at least five years old.
Could I still use the powders? And if so, would there be any loss in quality?