I was given some PYRODEX RS that is still sealed, and a can of elephant black powder that has a date code of 1994. Is this stuff still good ?

They should be fine. BP is not a chemical compound, just a mixture of charcoal, sulfur, and saltpeter. Kept dry it's virtually immortal. Pyrodex is a different critter, and it can degrade, but sealed and stored somewhere without tremendous temperature extremes it should last as long as any smokeless powder -- which is to say a long, long time.

pisgah nailed it. I've got some pyrodex that's 10 years old and shoots fine.

I have some 20 year old stuff both kinds that shoot fine too.( long ago I stocked up on FF, FFF, RS and P. )

If I'm not mistaken, either in the book or on the Hodgedon website you'll find information on the shelf-life of Pyrodex and/or the warning signs to look for if something is wrong with it. T-7 will get a nasty smell, much worse than what it has new, if it is degrading. I don't know if cold hurts it but heat will definitely destroy T-7.

As Pisgah said, black powder that is kept dry is immortal. I know people have found various amounts of black powder in cans and horns that is very old, well over 100 years, and as long as it didn't get wet/damp, it's still good.

Even if BP gets wet, if you dry it out it will work.