I've also had the problem with Dektol powder oxidized in the envelope. In general, you can tell by the color of the mixed stock solution (both film and paper developer) whether it is worth going further. If the stock solution is dark brown, it is definitely oxidized, and it is your call whether to test it further or throw it out. I might test print developer, I wouldn't risk film. If the color is still light, you are good to go.