A good example of how that doesn't matter is apple butter, which replaces neither peanut butter, or regular butter, and doesn't really resemble either, and which I've never seen anyone complain about the naming and the FDA will not go after any producer who makes it and labels it apple butter.
However I daresay you'd get in a bit of trouble if you took margarine and added a tiny bit of peanuts OR apple and then called it (very small "peanut" very large BUTTER).