Why wouldn’t your setting have potatoes? Does your setting have Peru in it? No, no Peru? Gee, then it sure sounds to me like you get to decide where potatoes come from in your setting; they don’t have to be a “new world” food if you world doesn’t have or has a different “new world.”
Sausage (at least forcemeat in casing) dates to Mesopotamia, 3000BCE.
I don’t think the innovative leap to put that sausage in between bread is a world-breaking defiling of historical accuracy, personally.