If you'd stored it in a hot attic, I'd say there would be reason for concern. But since it's been in a cool environment without major temperature swings, I'd expect it to work.
I have some S-05. On the packet it instructs me as so: "Store in a cool, dry place."
Sounds pretty much how you've stored it.
**************
Expiration or best-by dates are funny things. They are the dates before which the manufacturer wants you to use the product to guarantee a satisfactory result or, in the case of food, taste and aroma. But they're conservative; the real date is further out.
A friend of mine had an old beer kit sitting around for years, even going through a move that changed its location. He decided to brew it, using the packet of dry yeast that came with it.
The yeast worked. Now, I'm not vouching for how it tasted as I never tried it, but it produced beer and he seemed OK with the result. His was the first brew day I ever witnessed and even then I thought he did some things questionably, including using bleach to sanitize, and then rinsing off the bleach with tap water drawn from his well.
Still, the yeast worked.
Yours will, too. Just be sure to rehydrate it to give it the best chance.
