If they are kept frozen, they won't actually spoil. But the quality will deteriorate. "Freezer Burn" doesn't make something unsafe, it dries out the flesh and messes up the texture. So while they won't harm you, the shrimp may seem dry and/or tough.
Vacuum packaging or other airtight method will prolong them in the freezer, but if they had much exposure to air in their package, they are more subject to freezer burn.
I probably wouldn't toss them, I'd just be selective in how I prepared them. They won't be as good as when you first bought them, so shrimp cocktail is out. But preparing them in a sauce or adding them to a soup or gumbo, or a saucy pasta dish or casserole would be just fine.