If it was cooked with the poop inside then the doodoo particles are everywhere in it. You gotta take that shyt out before you cook it but OP already addressed this issue as out of his control. That being said, I've worked in kitchens and deveined hundreds of shrimp at a time. It's doable, just time consuming but I got really good at doing it fast.
hate it with a passion. Shrimp antenna everywhere.
when you do that and fry it right. Or put it in some pasta or bbq them.