Yes, provided it's not contaminated by something in the water. One of the manufacturers still compares newly manufactured lots to one of the 100+ year old lots that is stored in DI water to preserve it. It is removed from the water, dehydrated and test fired. Then they run the same test on the new lot to compare. I think the powder is is Bullseye? Maybe 2400? I forget which one. Powder doesn't really have a shelf life and if stored properly will easily go past 100 years and still be as good as the day it was made.
I have heard that same thing, they were talking about Bullseye.
I would take one round out of each box, dry them as best you can then test fire them. If there are problems, I will help you pull them and reload.