Shepherd moons are natural satellites near the edge of a planetary ring that have an influence on the shape and size of the ring due to their gravity. So it is possible for a satellite to be near the rings without being actually a shepherd. For instance, Pandora is on the outer side of Saturn's F ring, but isn't involved in shaping the ring, so it isn't a shepherd. On wikipedia, it says that we can't know if Cordelia and Ophelia are shepherds or not (I haven't found the reference for that yet, though) because we need better observations.
How many satellites in the Solar System do we know are shepherds?
