Last month I started using a what was left of some Grease Eraser that I had put away back in 1988 (the label indicates it was made in 03/88). I first washed work towels and it worked great, then I used it on trashed carpets, then all the other jobs that I would use a freshly bought batch. 22 year old powder, just a little clumpy but dissolved well. About 30 pounds was there from a 50 pound cannister so why not?
I've found that most cleaners, solvents, defoamers, etc have a shelf life that can span many years if sealed up properly.