The anchors that Rustdoc generates for multiple implementations of a trait (like Add for multiple different rhs) always point to the first implementation.
If you take a look to rust-sfml Vector2f, it implements impl Add<f32> for Vector2f and impl Add for Vector2f. But both anchors are the same:
http://www.rust-sfml.org/doc/rsfml/system/vector2/struct.Vector2f.html#method.add
You can't link to the second implementation...